Trojan Targets Skype Users

After making a big splash in the news through its $2.6 billion deal with EBay, Skype Technologies is getting more worrisome network chatter in the form of a malicious Trojan horse that is circulating as an e-mail attachment and purports to be the newest release of the company's Internet telephone software.

The e-mail, claiming to contain version 1.4 of Skype's voice over Internet Protocol (VOIP) software client, contains a variant of the IRCbot Trojan horse, according to MessageLabs, which issued a warning earlier this week after detecting and blocking hundreds of copies of the new variant.

Skype released its newest version on October 10.

How Trojan Works

Users who launch the attachment see a fake "installation error" box on their screens, according to MessageLabs. What is actually happening, however, is that the malware is installing itself, altering the registry and shutting down shared access and Microsoft Windows update services. It then tries to connect to an Internet Relay Chat (IRC) server but fails.

Although the Trojan is not widespread, it is still circulating, according to Alexander Peters, an antivirus researcher at the German subsidiary of MessageLabs.

Skype is concerned about the incident. The company said in a statement that it doesn't use e-mail to inform users the latest version of its software but does use digital signatures to ensure that its software releases are valid.

Users can verify the authenticity of Skype software by confirming that its digital signature is valid, the company said. Instructions for checking this are described in the Skype Administrator's Guide.

Wormy Trends

An ever-growing amount of unsolicited e-mail, or spam, contains malicious software, as criminal groups seek to infect computers with malware in order to add new systems to their botnets, or zombie networks, used illegally to distribute spam, Peters said.

"These groups are always looking for machines to keep their networks alive," he said. "It's a huge problem, and spam, which today is almost inseparable from malware, is at the heart of it."

"What has drawn attention to this particular Trojan--and not the many other Trojans out there in cyberspace--is the fact that this malware is part of a well orchestrated phishing attack based on a very convincing e-mail that uses the name of a widely familiar company and a timely occasion: the release of a new software version," Peters said. "Users should never open attachments from untrusted senders."