Microsoft hack update - worm most likely cause

Paul Rogers, network security analyst at MIS Corporate Defence Solutions, said: "From what we know, the most likely scenario is someone sending a QAZ worm attachment to an email which a Microsoft employee opened. Once opened it could send passwords and other information to an external email address."

Rogers believes the attack could be external or could come from a disgruntled employee. Most companies would have a block on executable email attachments from outside the company. But this could be waived for some departments, like developers.

It's also possible that an upgrade to the network left an area vulnerable - hackers routinely scan companies looking for weaknesses caused by such actions. An unhappy employee or ex-employee may have deliberately helped the hackers gain access to the system.

John Cheney, MD of Activis, said: "Most hack attacks come from inside a company and lots of people love to hate Microsoft. Microsoft needs to monitor its internal network for intruders."

Microsoft has still not confirmed if source code for its software has been stolen, nor has it confirmed rumours that the information was sent to an email account registered in St Petersburg, Russia.