Sophos warns of fake Microsoft security Trojan

A new campaign by malicious hackers uses a Web site designed to look like Microsoft 's Windows update page to trick unwitting Internet users into infecting their computers with a Trojan horse remote access program, according to anti-virus experts at Sophos.

The scam uses e-mail messages that appear to come from Microsoft to get recipients to visit a Web page that uploads the malicious program. Using the promise of Windows software patches to distribute malicious code isn't new. However, the latest attacks show that scammers are adopting strategies used by phishers to evade detection by gateway and desktop anti-virus programs, said Graham Cluley, senior technology consultant at Sophos.

The attack was first detected on Thursday in Sophos' Vancouver, Canada, lab after it was distributed in a spam campaign. The messages have subject lines like "Update your windows machine" or "Urgent Windows Update," Cluley said.

A link in the body of the e-mail message appears to take users to the Microsoft Windows Update Web site, but actually forwards them to a Web site operated by the attackers that installed a Trojan horse program called DSNX-05, according to Sophos.

The Web site run by the hackers was registered to an ISP in Toronto, but has since been shut down. The site looked very much like the actual Microsoft Windows Update page, and displayed Microsoft's corporate logo. One giveaway that something was amiss was that the URL displayed in the Web browser address bar showed only the IP address of the site, instead of the Windows update address, Cluley said.

Sophos does not know how many Internet users may have fallen for the ruse, Cluley said.

The method of attack is similar to phishing identity theft attacks, which have become common in the last year. As with many phishing attacks, gateway anti-virus software does not detect the scam, because there is no malicious code in the e-mail. Destkop anti-virus software with spam detection could spot the e-mail, but only if an anti-spam definition for the attack had been created and the user had updated the anti-spam definitions for their product, according to Cluley.

Those behind the attack may have been trying to capitalize on anticipation of Microsoft's upcoming software security patch release next Tuesday, he said. On Thursday, the Redmond, Wash., company said it intends to put out a number of security patches for its software.

"It's such a shame that, just as we're beginning to teach people more about security updates, cybercriminals are exploiting that," Cluley said.

Sophos warned that Microsoft does not issue security warnings in the manner used by this attack. E-mail users should be on guard when receiving an unsolicited e-mail that contains an attachment or asks the reader to click a link to a Web page, he said.

While the Web page used in the latest attack was disabled, those behind the scam could post the content in a new location and restart the attack, he said.

"It's hard being an average Internet user. You just can't trust anyone," Cluley said.

The IDG News Service is a Network World affiliate.