SEATTLE/SAN FRANCISCO (Reuters) - Microsoft Corp. (MSFT.O: Quote, Profile, Research) on Tuesday said a critical flaw in most versions of its flagship Windows operating system could allow attackers to run malicious programs on personal computers. In its monthly security bulletin, the world's largest software maker warned that Windows NT, Windows 2000, Windows XP and Windows Server 2003 were at risk and offered software updates to fix the flaws, which were given Microsoft's highest severity rating of "critical." "It does affect all (current) versions of Windows," said Stephen Toulouse, security program manager for Microsoft's Security Response Center. "We're not aware of...