Microsoft fell prey to a hacker attack discovered on Wednesday, in which source code for the company's most valuable software, including the newest versions of Windows and Office, was stolen, according to a report in Friday's edition of The Wall Street Journal (WSJ) newspaper.

Microsoft and the Federal Bureau of Investigations (FBI) - who were contacted by Microsoft on Thursday -are already investigating the hacker theft which is believed to have been initiated in St. Petersburg, Russia.

The company's security staff discovered that passwords were being remotely sent to an email account in Russia where the 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 WSJ said.