Microsoft is warning customers that crooks are exploiting an unpatched security flaw in Windows 2000 Server and Windows 2003 Server. The company says that an attacker could exploit the hole by sending a specially crafted RPC packet to an vulnerable system. The attacks target Windows 2000 Server and Windows Server 2003 systems through a hole in the Domain Name System, or DNS, service, Microsoft said in a security advisory. The attacks happen by sending rigged data to the service, which by design is meant to help map text-based Internet addresses to numeric Internet Protocol addresses.

While it works on the fix, Microsoft suggests several work-arounds for users of affected Windows versions. These include disabling remote management over RPC capability for DNS servers, blocking specific data ports using a firewall and enabling advanced filtering. Windows XP and Windows Vista are not impacted by the DNS flaw. Windows 2000 Server Service Pack 4, Windows Server 2003 Service Pack 1 and Windows Server 2003 Service Pack 2 are vulnerable, Microsoft said.