A quick & dirty guide to malware (part 2: viruses)

A dialogue screen shown by Virus:W32/Duts.A

This is the second posting in a three-part series covering common threats a user may encounter.

This series serves as a rough and ready guide, highlighting key features and trends relevant to most users.

The One That Left

Last week I spoke of Trojans, Viruses and Worms as The Big Three. I lied a bit, though. Viruses – as a distinct malware type – probably shouldn’t be on that list any more.

Viruses have always loomed large in users’ minds as the poster child of malicious programs – heck, we even call it the anti-virus industry. In the last 10 years or so however, the number of virus infections has nosedived; our Labs, which once dealt with viruses routinely, now sees a proper virus infection about once or twice a month. Today when people talk of ‘viruses’, more often than not what they’re describing is technically a trojan or a worm, and they’re using the term in a general, ‘any malware will do’ kind of way.

That’s not to say viruses are extinct; we still receive a small, if persistent, number of queries about viruses. This may be because many businesses, households and users (both in developed countries and in recently connected developing ones) still use old, out-dated, unpatched machines or programs, or haven’t yet developed a security-conscious habits.

Whatever the case, virus infections will probably still cling on to life for a weary day after, so let’s take a look at them.

Highlights of a virus

Definition of a virus given by Merriam-Webster online dictionary

The Merriam-Webster online dictionary’s bare-bones definition of a computer virus touches on important elements most users should know, so I’ll just elaborate a bit more on some key concepts:

“usually hidden within another seemingly innocuous program”

Last week I compared a virus to a parasite, because not only does it ‘hide’ in another program, but also depends on its host to function. For the virus to run, the unsuspecting user must actively launch the infected program, which in turn launches the virus.

For this reason, virus writers usually create viruses that infect executable files (especially popular programs such as word processors or media files), which have a higher chance of being run; programs with files that get passed around a lot are extra attractive, since they can affect even more potential victims.

A good example is the Microsoft Office suite which, with their huge community of business and personal users, used to be a popular target for macro viruses. We still see queries related to this virus type, though thankfully far less than previously.

“Produces copies of itself and inserts them into other programs”

If you think of the common cold virus spreading from one person to another, you’ll have a pretty good idea of why this behavior can be so damaging. When a infected file is executed, it searches for and infects new files; if the newly infected files are launched, they find and infect new files in turn, like some evil Multi-Level Marketing operation. At worst, this pattern can lead to every targeted file on the system being infected.

“Usually performs a malicious action”

The damage a virus can do by replicating and infecting new files is bad enough; its payload, a completely separate set of nasty actions, can be worse. The range of actions a virus can take is huge – connecting to a remote site, changing the desktop wallpaper, displaying silly notification messages, deleting data files…it really just depends on the virus author’s imagination and programming skills.

If you’re lucky, they’re not that good and you get failed viruses like Virus:W32/Stardust; if they’re good, then you get really nasty beasts like Virus:W32/Virut or Virus:W32/Sality.AA (one of the few viruses we still find regularly active).

Appending, prepending, cavity…who cares?

A dialogue screen shown by Virus:W32/ZMK

With thousands of unique viruses out in the wild, antivirus companies find it necessary to divide them into sub-types. Unlike trojans though, viruses don’t fall into neat categories reflecting their actions; instead, they naturally fall into groupings based on technical differences in the way they infect a file – which is  basically gobbledeegook to a user not interested in detailed analysis.

Gnerally, viruses can be divided into two groups – system infectors and file infectors. The majority of viruses are the latter and infect programs or data files. System infectors on the other hand write their malicious code to specific, critical sections of the hard disk containing the operating system, so that while the OS is running its normal routines, it’s also unintentionally executing the virus code.

Fortunately, for most users a virus’s classification is largely academic. For better or for worse, the sheer variety of possible effects each unique virus can have on a file or system makes it more practical to take each virus on a case by case basis.

Back to what’s important – why should the user  care?

So let’s go back to the original question that sparked off this series: do you really need to know if it’s a virus – as opposed to, say, a trojan or worm – infecting your computer?

Well, it helps to know because the two malware types tend affect your data and computer in different ways. As a (very) general rule, trojan infections is more about data theft and loss of control over the computer; virus infections tend to result in software disruptions or damage.

Trojans may copy and steal your data, but they don’t usually destroy the data file itself; they may stop programs from running but they don’t destroy the program. A virus on the other hand, insert its own code into a program or data file, and depending on how it does so, may either leave the host completely unharmed and functional, slightly disrupted, or completely non-functional.

Another difference between trojans and viruses that really affects the user involves disinfection. For one thing, a trojan is usually a single, discrete program – getting rid of it tends to be fairly simple, a matter of removing the malicious file and its residuals (registry keys, processes, icons, etc). Removing the trojan also generally doesn’t affect the integrity of other files on the computer.

Viruses are far more nebulous by design – they can be present in multiple files, in different locations. Identifying a virus-infected file may require scanning the entire computer to be sure every affected file is caught. Removing malicious code from an infected file or – if it can’t be saved, deleting the infected file entirely – can also be problematic if the damaged data is important or the program is a critical system component.

And this doesn’t even take into account the virus’s payload, which can produce a whole other set of worries.

If you’re still interested

Still, there is a ray of hope. If current malware trends persist, we may soon see adware or backdoors promoted to being the newest member of The Big Three, and viruses – as a distinct malware type – can finally be relegated to joining 3½” floppy disks in Computer Hell.

In the meantime, here’s some links to other, more in-depth resources on viruses:

Or partially available on Google Books:

  • “Elements of Computer Security” by David Salomon
  • “Cybercrimes: A Multidisciplinary Analysis” by Sumit Ghosh


Coming soon – Worms!

More posts from this topic

Mikko Hypponen

Mikko Hypponen’s Malware Hall of Fame

Mikko Hypponen is one of the world’s most prominent cyber security experts. Described as a “virus hunter” in a Vanity Fair profile called “The Code Warrior”, Hypponen has spent nearly 25 years with F-Secure protecting people from computer viruses, worms, trojans, and other types of malware. In 2011, Hypponen travelled to Pakistan to meet the men behind the first known PC virus – Brain.A. [youtube https://www.youtube.com/watch?v=lnedOWfPKT0&w=560&h=315] The Brain virus was released in January of 1986, making January 2016 the 30th anniversary of this milestone in malware history. I thought it would be interesting to reach out to Mikko and ask him about other families of malware that standout as being noteworthy. So here’s Mikko’s list of some of the most infamous malware families (including viruses, worms, trojans, etc) that’ve pestered, frustrated, and even extorted computer users over the past few decades. 1990 Form – Form was a common computer virus identified in 1990, and for several years, was arguably the most prominent computer virus in the world. Spread through 3.5” floppy disks, it infected millions of computers throughout the world, and is possibly one of the most widespread viruses in history. 1992 Michelangelo – Michelangelo earns a place on the list for being the first truly global virus scare. It was named after the famous artist because the virus remained dormant until March 6 (the artist’s birthday), when it would awaken and overwrite sections of infected hard disks, thereby making the information inaccessible and the computer unusable. The virus was never particularly prominent compared to some of its contemporaries, but its destructive nature and subtlety helped spread Michelangelo Madness throughout the globe. 1995 Concept – Concept was the very first macro virus – a type of virus that infects applications such as Microsoft Word. It was a very prominent security concern in the mid-nineties, and even though it was successful in propagating itself organically during this time, it hasn’t been seen in over a decade. As the first macro virus, it was notable in that it spread by hiding itself as a Word doc and then infecting computers as those documents were shared. By using Word, it could use both Windows PCs and Macs to spread infections, as the software could run on both platforms. 1999 Melissa – Melissa, supposedly named after an exotic dancer, was a computer virus that sent infected Word documents to contacts in victims’ Outlook address book. While the virus was not designed to be particularly destructive, its rapid proliferation through the Internet wreaked considerable havoc on corporate servers and infrastructure. Some accounts claim that it infected twenty percent of computers globally, and the man eventually convicted of releasing the virus into the wild admitted to causing eighty million dollars in financial losses. 2000 Loveletter – Loveletter, also widely known as ILOVEYOU, was a prominent email worm that was able to spread itself throughout the globe in a matter of hours by promising victims a little bit of love. Disguising itself as a chain, love-themed email to recipients helped it quickly spread from its Filipino origin through Asia, Europe and North America. To this date, it is one of the largest malware outbreaks of all time, and responsible for an estimated 5.5 billion dollars of damage. 2001 Code Red – Code Red was the first fully-automated network worm for Windows. As in users would not have to interact with a machine in order to spread the infection. Code Red’s most infamous day was July 19th, 2001, when it successfully infected 300,000 servers. The worm was programmed to spread itself on certain days, and then execute distributed denial-of-service (DDoS) attacks on others, and was used against several different targets (including The White House). 2003 Slammer, Lovsan, and Sobig – Ok, so there’s three here and not just one. But they all occurred very close together, and unfortunately, all three were worms responsible for massive, global malware outbreaks. Slammer targeted servers so it’s presence wasn’t readily apparent to end users (save some lagging when they were attempting to access an infected server). Lovesan, however was able to infect end users running Windows ME or Windows XP, and use the infected machines in DDoS attacks. Sobig spread itself through email and network drives, and contained a trojan in order to cause more headaches for infected users. However, it appears that the trojan feature did not function as expected. These three worms infected millions of machines, and made headlines all over the world. 2004 Sasser – A computer worm that can be considered as the last large “hobbyist” outbreak. This is significant as it signaled the end of an era when most malware was written by people who were simply curious to see what the malware could do. Nowadays, malware has a more specific, insidious purpose, such as stealing information or making money. 2006 Warezov – A two-year email worm campaign perpetuated by professional criminals, Warezov gained notoriety for downloading new versions of itself from remote servers – sometimes as frequently as every 30 minutes, according to a 2006 interview with Mikko. 2007 Storm Worm (also called Small.dam) – Storm Worm was a trojan that was spread as an attachment to spam emails. But more importantly, it was a combination of complex and advanced virus techniques that criminals were able to use to make money by using infected machines as part of a botnet. 2013 Cryptolocker – A notorious ransomware family, Cryptolocker was spread through malicious email attachments, as well as the infamous Gameover Zeus botnet. Infected victims would find their hard drives suddenly encrypted, essentially locking them out of their devices and data until they paid a ransom to the perpetrators. While the FBI, in cooperation with other law enforcement agencies and security companies (including F-Secure), were able to disrupt the operation, the perpetrators were able to use Cryptolocker to extort about 3 million dollars from victims before being stopped. Other notable mentions include the 2005 Sony rootkit (for being distributed on Sony BMG CD-ROMs on their behalf), the still prominent Downadup worm from 2008 (for infecting millions, including armed forces of several countries and police departments), and the well-known Stuxnet virus from 2010 (for both its sophistication and its apparent state-sponsorship). If you want to know more about the history of computer viruses, you can check out Computer Invaders: The 25 Most Infamous PC Viruses of All Time!

January 29, 2016

Yes, it’s OK to play with scammers

This TED talk is so hilarious that I just have to share it with you. Watch it! British comedian James Veitch is engaging in the noble art of scam baiting, or scamming the scammers. The same as this site is dedicated to, or when I almost sold my boat to Mexico. I guess most or all of you already know how to spot an advance payment scam, aka. Nigerian scam. But James has some more to offer here. He’s making two important points, in addition to the excellent entertainment value. People often warns about engaging in any kind of conversation with these scammers. They are after all criminals and it’s safest to steer clear of them. I disagree, just like James. The people behind this kind of scams is not exactly the violent drug mafia. As a matter of fact, anyone who can use e-mail and Google Translate can set up a scam like this. And they are located in some poor remote country, typically in Africa. So it’s extremely unlikely that any of them would start hunting down people who play with them. That would disrupt their everyday business and cut profits, cost money and introduce the risk to get caught. But I do discourage people from engaging in scam baiting under their real identity. Set up a new mail account under a false name and never reveal any real contact info to them. You can reply from a different address than where you got the original spam. They are pumping out millions of spam messages and will not even notice the changed address. This adds an additional layer of security. And more important, it keeps your real inbox free of spam. Use their own tactic. Create a false identity with name, address, profession and country of residence. Stick to that story and make sure not a single bit of it is true. Read more about how to scam bait at 419eater.com. The other point is that scam baiting is a good deed. It keeps the scammers busy and ties up their resources. Resources that otherwise would have been used to scam a real victim and cause real damage. A single scam baiter can’t of course save the world, but they would probably shut down if all of us spent an hour a week scam baiting. And it can be fun so why not? A good scam baiter can be a real pain in the a** for the scammers. Be prepared to get some threats and evil language when they realize what is going on. Consider that as a trophy, a proof that you did it right. Don’t feel bad for them. They did after all contact you with the sole purpose to scam you for money.   Safe scam baiting, Micke   Image: Screenshot from ted.com  

January 28, 2016