Source code to some of Microsoft's most valuable software has been stolen during a hacker attack on the company.

The newest versions of Windows and Microsoft Office have been stolen, says a report in Friday's Wall Street Journal.

Microsoft called in the FBI yesterday. The hacker theft is thought to have come from St Petersburg in Russia.

Alarm bells rang when Microsoft's security staff discovered that passwords were being remotely sent to an e-mail account in Russia. The Russian hackers then posed as Microsoft employees working off-site from Microsoft's Redmond, Washington headquarters, to gain access to sensitive areas within Microsoft's internal network, the report said.

It is believed that no alterations were made to Microsoft software codes and that the attack could possibly be one of the first "data hostage" cases, where hackers hold a corporation's intellectual property hostage, threatening to make code public unless their demands are met, the Wall Street Journal said.