The social network for microblogging service Twitter has been hacked and is pumping out pop-up messages and links to porn sites.

Initially, the virus required not a click, but only a move of the mouse over a message containing a link and it opened in the browser.

The BBC has reported that the virus was spread by worms, self-replicating and malicious piece of code.

However, the flaw that caused the pages to open automatically has been fixed. The link still exists but now users have to click on it in order for it to appear.

Users are advised to use third-party Twitter client, such as TweetDeck, rather than the website Tweeter.com, until the flaw is completely fixed.

According to the BBC, this is not the first attack on Twitter.

In April 2009, another worm spread links to rival site, again showing unwanted messages on infected user accounts, the BBC reported.

Users could delete an already published message containing the dangerous link by going to http://www.accessibletwitter.com/ and deleting the unwanted messages.