According to a criminal complaint [PDF] filed by prosecutors, Russian national Alex Kibkalo faces criminal prosecution in the US over allegations he leaked pre-release versions of Windows 8 to a French blogger.

Kibkalo, who worked for Microsoft in Lebanon and Russia, allegedly turned against Microsoft after working for the firm for seven years and scoring a poor performance review.

An FBI special agent revealed details of an internal investigation by Microsoft: Microsoft looked through their systems and uncovered evidence that Kibkalo had emailed the blogger's Microsoft-hosted Hotmail account to leak "proprietary and confidential trade secrets."

Kibkalo allegedly uploaded pre-release software updates for Windows 8-powered devices, a copy of the Microsoft Activation Server Software Development Kit, and unreleased versions of Windows Live Messenger to his personal Windows Live SkyDrive account.

The court in Washington was told that access to the development kit would be a boon for hackers trying to reverse-engineer the code used to thwart software piracy,

A Microsoft spokesman said in a statement to reporters: "We take protection of our intellectual property very seriously, including cooperating with law-enforcement agencies who are investigating potential criminal actions by our employees or others."

The case is filed as USA v. Kibkalo in the Western District of Washington.