Alert over online chat software

Experts today called for millions of computer users to remove online chat software.

They say hackers are using it to attack websites or spread viruses.

The IM software, or Instant Messaging, is hugely popular with home users and companies - more than 40 per cent of British companies use it instead of email to communicate internally.

It allows people to chat in real time over the internet and to send pictures and files.

IM software is produced by Microsoft, Yahoo! and AOL.

Hackers have created a new breed of intelligent "chatbots" that masquerade as people, while in the background spreading a virus.

The technique is also being used to remotely control networks of hijacked computers, which have attacked dozens of betting sites.

Jason Hart, of computer security firm Whitehat UK, said: "The chatbot could send itself to 10,000 addresses, which could then attack one site." Known as a denial of service attack, the computers simply overload the web server, causing it to crash.

Mr Hart says the only way to stop the spread of chatbots is to remove the software.