The Dutch hacker, using the alias 'Dimitri,' said that Microsoft failed to install a patch for a known bug in its Internet Information Server (IIS) software, and has not sufficiently secured its Web servers, he said in an interview with the IDG News Service.
He gained access to several of Microsoft's Web servers and was able to upload a short text file, "Hack The planet," boasting of the hack to http://events.microsoft.com/, Dimitri said. He could alter files on Microsoft's download site, he said.
"I could add Trojan horses to software that MS customers download," Dimitri said.
Dimitri also claimed that he downloaded files containing administrative user names and passwords to the server. The encrypted files could be decoded with a tool called the L0ft crack, he said, but added that he had not and would not decode them.
Dimitri said he got a "pretty good look" at Microsoft's server structure. He said the server domain is called Houston and that all of Microsoft's Web servers are set up the same way with the same disk image.
A Microsoft spokesman confirmed that the hacker reached at least one server, but said that Microsoft security personnel were rechecking their servers for holes to patch.
"We investigated this report," Microsoft spokesman Adam Sohn said. "He was able to exploit a known security flaw that we were able to patch. The patch had not yet applied to the server." He could not confirm that all servers in Microsoft's network had the hole patched.
The server was in semi-retirement, redirecting visitors to another area of the network with more updated content, he said. "The whole purpose of it was a redirect server. Before, it hosted events content. It had recently been retired from its former uses. ... It wasn't really hosting any content at all."
"We are very focused on securing and maintaining the servers on our network," Sohn said. "From a security standpoint, there should be no difference between servers."
He conceded that the size of Microsoft's network -- and the allure to hackers of breaching Microsoft's security -- make defending its systems an ongoing challenge. "Microsoft is a high-priority target. There is always a possibility that hackers can get into any network. ... There are bad people out there that will try to do bad things.
"Would we prefer that our people put patches in on the same day they come out? Sure," Sohn said. "It's hard to give you an absolute certainty that the patch had been applied across the board. Given today's incident, our security teams are going back to check out the systems."
Dimitri said that he used the so-called Unicode bug to get access to Microsoft's systems. Microsoft first patched this security hole on Aug. 10, and issued a security bulletin on Oct. 17 pointing customers to the same software patch. On its TechNet Web site, Microsoft refers to the bug as the "Web Server Folder Traversal" vulnerability.
"It is extremely sloppy for Microsoft not to install its own patches," Dimitri said.
Sohn said the security flaw was unrelated to the intrusion Microsoft reported to the US Federal Bureau of Investigation (FBI) on Oct. 26. In that case, hackers gained access to source code under development for an unidentified future product. The team patching the security hole in the server is different from the one working on the October intrusion, which was achieved using an attack program hidden in e-mail, said Rick Miller, another Microsoft spokesman. "They had nothing to do with each other. It's like comparing apples and oranges."
However, two hack attacks revealed in one week have raised questions about the extent of the weaknesses in Microsoft's computer defenses. Security experts who have been able to confirm the intrusion through access logs provided by Dmitri said Microsoft must tighten its defenses.
"It's bad enough that we can browse the contents of their server, they shouldn't be vulnerable to this," said Ryan Russell, technical editor of Securityfocus.com Inc., a computer security Web site. "If they had anything interesting on the server, he could have gotten into it."
The damage to customer confidence may outweigh the actual security damage to Microsoft.
Dimitri "didn't have to be a rocket scientist" to get into Microsoft's server using a known security bug, and theoretically he had the opportunity to do damage once achieving access, said Paul Zimski, a security researcher at Internet security firm Finjan.