Hackers’ve publicly released new attack code that exploits a critical bug in the Windows operating system, putting pressure on Microsoft to fix the flaw before it leads to a worm outbreak. The vulnerability has been known since Sep 7, but until today the publicly available programs that leverage it to attack PCs haven't been able to do more than crash the operating system. A new attack, developed by Stephen Fewer, lets the attacker run unauthorized software on the computer, in theory making it a much more serious problem. When he ran it on native Windows systems, it simply caused the machines to crash. The attack "definitely works on at least some physical machines, but looks like it could use more testing," Moore said. Either way, the public release of this code should put Windows users on alert. Security experts worry that this code could be adapting to create a self-copying worm attack, much like last year's Conficker outbreak, noted.