BadTrans is a malicious Microsoft Windows computer worm distributed by e-mail. Because of a known vulnerability in older versions of Internet Explorer, some e-mail programs, such as Microsoft's Outlook Express and Microsoft Outlook programs, may install and execute the worm as soon as the e-mail message is viewed. Once executed, the worm replicates by sending copies of itself to other e-mail addresses found on the host's machine, and installs a keystroke logger, which then captures everything typed on the affected computer. Badtrans then transmits the data to one of several e-mail addresses.