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A CDE Definition

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An email virus that exploits a vulnerability in the Internet Explorer browser and executes when the message is read or previewed. Possibly originating in China, several versions of the Klez worm have been introduced since late 2001. They deposit themselves in the PC's Windows directory with a random file name and set the Registry to launch at startup. Klez searches for email addresses in the infected machine, and, using its own Internet mail transmitter (SMTP engine), sends messages to those addresses with virus attachments and a variety of subject headers and body text. Thus, the same user can keep getting different Klez emails from the same source.

In addition, Klez grabs an email address in the infected machine and turns it into the "from" address. If your PC is virus free, but you get emails from others saying you are constantly infecting them, those emails are coming from some other infected PC that has your email address somewhere in the computer (address book, old message, etc.). In addition, if you keep getting returned, undeliverable messages you never sent, an infected PC is sending emails using your from address to recipients whose mail addresses are no longer valid. See email virus.

email virus

A virus that comes within an file attached to an email message. When that file is opened, the virus does its damage. Macro viruses can come in Microsoft Word documents that are sent as email attachments. The macro causes the damage when the document is opened providing macro processing has not been disabled within the Microsoft Word application.

Look at Your Extensions!
Files with .EXE or .VBS extensions are always suspect, because once the file name is clicked, the program is run, and it can do anything it wants within the computer. SHS files, a somewhat obscure file type, can also contain executable code. Another approach is to attach a Windows link file (.LNK), which is a shortcut, or pointer, to an executable file (.EXE) that is also attached. Since many have been warned not to click an .EXE attachment, the link file is a sneaky way of launching the .EXE file for unaware users. See dangerous extensions, email bomb, virus, Klez, Worm.ExploreZip virus, BubbleBoy virus and SHS virus.

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