Bugbear is “a destructive mass-mailing worm” that spreads via shared networks and by e-mailing itself to those in a victim's local address book. Once Bugbear infects a system, it will attempt to terminate the process of the system's security programs.
It then copies itself into the Window Directory System as a random executable file and monitors every keystroke, encrypting and storing the captured information. The stolen data can then be e-mailed to the virus writer or accessed by anyone using the infected machine.
Users of Internet Explorer versions 5.5 (the most prevalent version of Microsoft’s browser) and 5.01 are at risk.