• PC World
• »Security

A new version of the NetSky e-mail worm has begun circulating through the Internet, anti-virus software companies report.

The new worm is known as NetSky.C. Major antivirus vendors have all updated their virus definition files to detect and prevent infection by the new worm.

Similar Attack

Like its predecessor NetsSky.B, which struck last week, the worm arrives via e-mail messages with familiar subject lines like "Question," "Fwd: lol," and "Re: hey." Users launch the worm by clicking on attachments accompanying the messages.

"They're keeping subject messages really simple, which entices users to click on the attachment," says Steven Sundermeier, the vice president of products and services with Medina, Ohio, security software vendor Central Command. "You could see how that kind of piques users' curiosity."

Once launched, the worm then installs its own mail server on the user's computer and begins sending infected e-mail using addresses it collects from the infected computer.

The worm also appears to target users of file-sharing services, Sundermeier says.

"If it finds any subdirectory that has the word "shar" in its name, it will drop a long list of enticing filenames in it, which are copies of itself," he says. "That now makes it available through file sharing applications like Kazaa or instant messaging applications."

These infected files have a variety of names, including "Adobe Photoshop 9 full.exe," Microsoft Office 2003 Crack.exe" and "Dark Angels.pif," Sundermeier adds.

Fast Action

NetSky.C first appeared Tuesday night, says Patrick Hinojosa, the chief technology officer with antivirus vendor Panda Software in Glendale, California. By Wednesday morning, 3 percent of the users of Panda's on-line virus checking service were infected, he says.

"Three percent within one day is a pretty good clip, so this one looks like it's spreading a little bit faster than NetSky.B," he says.

The NetSky.C worm is very similar to its NetSky.B predecessor, but "B" uses different subject names, and searches for subdirectories with the word "sharing" instead of "shar," Sundermeier notes.

Another difference is that version C causes the user's computer to beep when the infected file is launched.

"It's kind of a computerish type sound," Hinojosa says. "That's a sure sign when you get it." Panda has posted a wave file demonstrating the sound.

NetSky.B displays a Windows error message saying "the file could not be opened," when it infects a computer, he says.