Skype users are under attack by a new virus that exploits the internet calling software's text-based chat feature, the company said Monday.

Skype, which is owned by auction website eBay Inc. and based in Tallinn, Estonia, said the attack begins when a Windows user receives a chat message with a link in it from someone in their contact list or an unknown user.

The chat message comes in several versions and is "cleverly written" to fool users, Skype blogger Villu Arak wrote on Monday. The virus, called w32/Ramex.A, will only infect a user's computer if they follow the link and download the related software, which is disguised to look like a JPEG picture. Infected computers will then send similar messages to other Skype users. In his post, Arak did not say whether the virus caused any other problems.

Skype said it had alerted several antivirus companies about the worm, adding that F-Secure and Kaspersky Lab have already updated their products to detect and remove it.

Skype, which celebrated its four-year anniversary two weeks ago and has nearly 220 million users worldwide, last faced major adversity when it suffered a massive outage in the middle of August. The company said the outage, which left millions of customers without its internet-based phone service, was caused when a large volume of users rebooted their computers to install a new Windows update.