8.3. Nondestructive Payload
Almost half of all computer viruses belong to this class. Many computer viruses simply display a message on the screen when they activate. Several such examples are given in previous chapters of this book. Virus writers and malicious code authors are often politically motivated. The WANK1 worm was a typical example of this. This worm was released on the SPAN network on October 16, 1989. The worm replaced the system banner, displaying the message shown in Figure 8.1 when a user logged in on a DEC system.
Figure 8.1. Message released from worm.
Other computer viruses, such as W95/Marburg, have graphical payloads. When Marburg activates, the virus loads the standard IDI_HAND (0x7F01) icon resource, which is used in case of serious error messages, and puts it on the desktop. Finally, it draws up to 256 icons at random positions on the desktop. (See Figure 8.2.)
Figure 8.2. The activation routine of the W95/Marburg virus.
Windows 95 will slowly redraw the desktop area when new windows are moved, causing Marburg's icons to disappear; however, the virus will draw new icons all over again.
Marburg is less annoying than old DOS viruses such as Cascade, which caused the characters to "fall down" to the bottom of the screen in a cascading effect, with some little noise in the background using the PC's speaker.
Probably one of the most infamous people in this category is the French virus writer, Spanska, author of the IDEA virus, which displays several animations, including the one shown in Figure 8.3. All viruses written by Spanska belong to the nondestructive payload category.
Figure 8.3. The activation routine of Spanska's IDEA virus.
Spanska's most infamous animation is displayed by W32/SKA (also known as the Happy99 worm and discussed in Chapters 3, "Malicious Code Environments" and 9, "Strategies of Computer Worms"). Some viruses are even interactive and play a game with the user. The Playgame virus is an example2.
Of course, viruses are not restricted to displaying animations and messages on the screen. They can use the speaker to play music or even to attempt to speak. On modern computers, playing MP3 or WAV files is no problem, and viruses take advantage of this. Some annoying viruses (and even backdoor Trojan programs) open and close the CD-ROM's door repeatedly, turning a computer lab into a "ghost house."
Figure 8.4. The activation routine of the W95/Haiku virus.
W95/Haiku also connects to 188.8.131.52 (www.xoom.com at the time of the virus attack) and uses the GET command to download a Windows WAV file (/haiku_wav/Haiku.wav). It saves this Windows sound file as c:\haiku.wav and plays it. Haiku demonstrates that the actual replicating code does not necessarily need to carry the payload within itself, making the virus much shorter.