Fears of a network worm attack targeting unpatched Windows 2000 systems heightened on Thursday with news that private security researchers have already reverse-engineered Microsoft's critical MS05-051 update to create proof-of-concept exploits. The MS05-051 bulletin, which shipped as part of Microsoft Corp.'s October batch of patches, includes fixes for four different Windows flaws, one of which is considered a major worm hole in the enterprise-heavy Windows 2000 operating system. That bug, an unchecked buffer in the MSDTC (Microsoft Distributed Transaction Coordinator), could be exploited by a remote unauthenticated user to take complete control of an unpatched system. "That one is really easy to exploit," said Marc Maiffret, co-founder and chief hacking officer at eEye Digital Security, the private research outfit that discovered and reported the vulnerability to Microsoft. "We are definitely going to see dangerous exploits for it because it's not really technically challenging to write the exploit code," Maiffret said in an interview with Ziff Davis Internet News.