Going back to the origin of viruses, it was in 1949 that Mathematician John Von Neumann described self-replicating programs which could resemble computer viruses as they are known today. However, it was not until the 60s that we find the predecessor of current viruses. In that decade, a group of programmers developed a game called Core Wars, which could reproduce every time it was run, and even saturate the memory of other players’ computers. The creators of this peculiar game also created the first antivirus, an application named Reeper, which could destroy copies created by Core Wars.
However, it was only in 1983 that one of these programmers announced the existence of Core Wars, which was described the following year in a prestigious scientific magazine: this was actually the starting point of what we call computer viruses today.
At that time, a still young MS-DOS was starting to become the preeminent operating system worldwide. This was a system with great prospects, but still many deficiencies as well, which arose from software developments and the lack of many hardware elements known today. Even like this, this new operating system became the target of a virus in 1986: Brain, a malicious code created in Pakistan which infected boot sectors of disks so that their contents could not be accessed. That year also saw the birth of the first Trojan: an application called PC-Write.
Shortly after, virus writers realized that infecting files could be even more harmful to systems. In 1987, a virus called Suriv-02 appeared, which infected COM files and opened the door to the infamous viruses Jerusalem or Viernes 13. However, the worst was still to come: 1988 set the date when the “Morris worm” appeared, infecting 6,000 computers.
From that date up to 1995 the types of malicious codes that are known today started being developed: the first macro viruses appeared, polymorphic viruses … Some of these even triggered epidemics, such as MichaelAngelo. However, there was an event that changed the virus scenario worldwide: the massive use of the Internet and e-mail. Little by little, viruses started adapting to this new situation until the appearance, in 1999, of Melissa, the first malicious code to cause a worldwide epidemic, opening a new era for computer viruses.
Until the worldwide web and e-mail were adopted as a standard means of communication the world over, the main mediums through which viruses spread were floppy disks, removable drives, CDs, etc., containing files that were already infected or with the virus code in an executable boot sector.
When a virus entered a system it could go memory resident, infecting other files as they were opened, or it could start to reproduce immediately, also infecting other files on the system. The virus code could also be triggered by a certain event, for example when the system clock reached a certain date or time. In this case, the virus creator would calculate the time necessary for the virus to spread and then set a date –often with some particular significance- for the virus to activate. In this way, the virus would have an incubation period during which it didn’t visibly affect computers, but just spread from one system to another waiting for ‘D-day’ to launch its payload. This incubation period would be vital to the virus successfully infecting as many computers as possible.
One classic example of a destructive virus that lay low before releasing its payload was CIH, also known as Chernobyl. The most damaging version of this malicious code activated on April 26, when it would try to overwrite the flash-BIOS, the memory which includes the code needed to control PC devices. This virus, which first appeared in June 1998, had a serious impact for over two years and still continues to infect computers today.
Because of the way in which they propagate, these viruses spread very slowly, especially in comparison to the speed of today’s malicious code. Towards the end of the Eighties, for example, the Friday 13th (or Jerusalem) virus needed a long time to actually spread and continued to infect computers for some years. In contrast, experts reckon that in January 2003, SQLSlammer took just ten minutes to cause global communication problems across the Internet.
Notoriety versus stealth
For the most part, in the past, the activation of a malicious code triggered a series of on screen messages or images, or caused sounds to be emitted to catch the user’s attention. Such was the case with the Ping Pong virus, which displayed a ball bouncing from one side of the screen to another. This kind of elaborate display was used by the creator of the virus to gain as much notoriety as possible. Nowadays however, the opposite is the norm, with virus authors trying to make malicious code as discreet as possible, infecting users’ systems without them noticing that anything is amiss.
Internet and e-mail revolutionized communications. However, as expected, virus creators didn’t take long to realize that along with this new means of communication, an excellent way of spreading their creations far and wide had also dawned. Therefore, they quickly changed their aim from infecting a few computers while drawing as much attention to themselves as possible, to damaging as many computers as possible, as quickly as possible. This change in strategy resulted in the first global virus epidemic, which was caused by the Melissa worm.
With the appearance of Melissa, the economic impact of a virus started to become an issue. As a result, users -above all companies- started to become seriously concerned about the consequences of viruses on the security of their computers. This is how users discovered antivirus programs, which started to be installed widely. However, this also brought about a new challenge for virus writers, how to slip past this protection and how to persuade users to run infected files.
The answer to which of these virus strategies was the most effective came in the form of a new worm: Love Letter, which used a simple but effective ruse that could be considered an early type of social engineering. This strategy involves inserting false messages that trick users into thinking that the message includes anything, except a virus. This worm’s bait was simple; it led users to believe that they had received a love letter.
This technique is still the most widely used. However, it is closely followed by another tactic that has been the center of attention lately: exploiting vulnerabilities in commonly used software. This strategy offers a range of possibilities depending on the security hole exploited. The first malicious code to use this method –and quite successfully- were the BubbleBoy and Kakworm worms. These worms exploited a vulnerability in Internet Explorer by inserting HTML code in the body of the e-mail message, which allowed them to run automatically, without needing the user to do a thing.
Vulnerabilities allow many different types of actions to be carried out. For example, they allow viruses to be dropped on computers directly from the Internet -such as the Blaster worm-. In fact, the effects of the virus depend on the vulnerability that the virus author tries to exploit.