AOL’s instant messaging service has been hit by a virus which downloads spyware onto computers via a special website.

The virus spreads via messages on AOL’s AIM software, either saying HILARIOUS!!! Or see thing!!!, with a URL. Clicking on the link takes the user to a web page that attempts to download a Trojan onto the computer using patchable flaws in the browser.

“We have seen several versions of the URL,” said web monitor Websense, which issued an alert about the virus.

“Some are up and some have been taken down. All have been hosted on personal web pages at ISPs, have had the extension of ‘.com’, prefixed by ‘~username’, and either ‘image’ or ‘pic’, followed by a number and extension.”

Once installed, the Trojan then modifies several registry items, adds a browser helper object, and installs several pieces of spyware. It also connects to more than 10 different websites to download and install other Trojan Horses and pieces of spyware.

AOL has become a regular target in recent months. Last month it was hit with a phishing scam, although the company claims that no information was stolen.