Microsoft

(MSFT) - Get Report

said last night that the company and the Federal Bureau of Investigation are investigating a break-in that officials believe resulted in hackers stealing the software maker's source code.

The company has been aggressively attempting to keep private its source code in a massive lawsuit with the Justice Department. And it is fighting a court-ordered breakup, which would split the company into two units.

TST Recommends

The break-in was reportedly discovered Wednesday when security employees for the Redmond, Wash.-based giant discovered emails being sent to St. Petersburg, Russia. The company's electronic logs determined that the information being sent was the company's code for its software products.

The motive behind the break-in is currently unknown, according to published reports. Unlike open operating systems like Linux, Microsoft has gone to great lengths to guard the source code of its products, which it views as a vital part of its intellectual property.

The stock closed at $64.44 yesterday, but it was not active in preopen trading this morning. It was down only slightly to $64 on very little action.