Authorities are investigating a computer attack on a U.S. military computer server that took advantage of a previously unknown flaw in a Microsoft Corp. program. The attacker accessed the Defense Department server last week through a machine running the Windows 2000 operating system and Microsoft’s Internet Information Server, which is used for displaying Web pages to the public. Once inside, the hacker began scanning computers linked to the compromised server and sending information back to an outside machine, said Russ Cooper, who runs a popular computer-security electronic mailing list. Full Story