The worm, dubbed Pykse.A, is similar to threats that affect instant-messaging applications. A targeted Skype user will receive a chat message with text and a Web link that looks like it goes to a JPEG file on a Web site, F-Secure said on its Web site.
Clicking the link will redirect the user to a malicious file. The file, after executing, will send a malicious link to all online contacts in a Skype user's list and will show a picture of a scantily clad woman, F-Secure said. In addition, it sets the user's Skype status message to "Do Not Disturb," the security firm said.
Pykse also visits a number of Web sites that don't host any malicious code and a site that appears to count infected machines, F-Secure said. The Finnish security company doesn't list any particular malicious payload for Pykse other than it spreading and visiting Web sites. The IM worm affects Skype users running Windows.
Such threats for Skype aren't new. Last month, miscreants. This threat also arrived with a Web link sent in a Skype chat message. Clicking on the link would result in a and the Trojan horse sending messages to the victim's Skype contacts.
In February, attackers also targeted Skype users with another Trojan horse that had propagation capabilities.
Skype has acknowledged in the past that its instant-messaging featurejust like any other IM service. Kurt Sauer, Skype's chief security officer, repeated that acknowledgment on Monday in a statement sent by the company's public relations agency.
"Harmful viruses and Trojan horses may damage a user's computer and collect private data, regardless of whether a person is using Skype, e-mail or other IM clients," Sauer said in the statement. "Skype strongly recommends that users take extra caution in general when asked to open attachments or links from unknown people, or suspicious-looking attachments even from people you know."
Skype also recommends using antivirus software to check the files received from other people.