A new mass-mailing virus, which disguises itself as a file sent by a computer user's network administrator, began infecting systems Friday. The worm, which is being dubbed "mimail," attempts to exploit a vulnerability in Internet Explorer that allows a script to be executed by an infected computer. The worm then tries to use that script to mass e-mail itself, potentially clogging mail servers or slowing down networks, according to antivirus company Symantec.

The arrival of Mimail comes amid heightened fears that a large-scale attack on the Internet could be looming. The federal government warned this week that a widespread flaw in Windows could be used to generate an attack. The e-mail that carries the worm has "your account" in the subject line, according to Symantec, and the body reads, "Hello there, I would like to inform you about important information regarding your e-mail address. This e-mail address will be expiring. Please read attachment for details." It is then signed "Best regards, Administrator" and contains an attachment labeled "message.zip" that carries the malicious code.