One of the most common ruses used by the writers of computer viruses to spread their creations to as many computers as possible is the use of images. They are sometimes used to grab users' attention and get them to open the infected files. On other occasions, it is quite the opposite: they serve to distract users while the virus is carrying out other actions, such as sending out messages en masse or deleting files from the system. Sometimes images are used simply as a kind of signature, so that victims can see that the computer has been attacked by a specific malicious code.
There are actually relatively few viruses that use images, given the fact that the size of such files can prevent the malicious code from spreading easily. This at least is good news, because these types of threats are often highly effective at infecting computers.
A wide variety of images have been used by virus creators, although the tendency to use sexually explicit pictures is well established. Recent examples of malicious code that exploit images include Tasin.C, which downloads and runs an erotic image of a well-known Spanish celebrity or Mugly.A, a worm that displays a grotesque face on screen.
Throughout the history of computer viruses there have been many others that use this ploy. Monopoly displayed a picture of the board of this famous game, but with a photograph of Bill Gates in the logo. The Fly produced a picture of a set of teeth with a squashed fly embedded in them. Other classic examples include Cookie, which interrupts users' work by showing a famous child asking for a cookie and Ambulance.760.A, a virus that caused a picture of an ambulance to go back and forward across the screen.
As mentioned before, images have sometimes been used for ends other than ensuring that the malicious code spreads across the Internet and can be designed to hide the real payload of the virus. For this reason many of them are simply imitation system error messages or dialog boxes. Along these lines, there have even been viruses using imitation corporate web pages such as Gimared.A, or Gibe.C, which displayed an image of the Microsoft website.
Similarly, virus authors have often resorted to startling images, possibly in an attempt to get people to pass them on to others. One example is GhostGirl, which, as the name suggests, displays a ghostly image of a young girl.
In any event, all users should ensure they have a good antivirus installed and updated, in order to deal with any such malicious images before it is too late.