U.S. authorities are examining how a computer hacker used a previously unknown problem in a Microsoft Corp. software program to access a Defense Department computer server last week, the Los Angeles Times said. The hacker entered the server through a machine operating Windows 2000 and Microsoft’s Internet Information Server, which posts Web pages for public viewing. The person scanned computers connected through the server and sent data to another machine, the newspaper said, citing Russ Cooper, manager of a computer-security electronic mailing list. A military official notified Cooper and Microsoft, which offered a software patch. Cooper said it was improbable that the hacker compromised the server significantly because the server wasn’t networked with computers containing sensitive data, the newspaper reported. Full Story