Microsoft security managers says companies should focus on backup and recovering

"When you are dealing with rootkits and some advanced spyware programs, the only solution is to rebuild from scratch. In some cases, there really is no way to recover without nuking the systems from orbit," Mike Danseglio, a program manager in Microsoft's security group, told a security conference in Florida.

Even though anti-virus technology is improving, Danseglio conceded that traditional approaches are failing in the face of more sophisticated malware and highly-motivated profit-driven virus writers. The threat has moved on from network worms towards Trojans and other forms of more difficult to detect malware. "Detection is difficult, and remediation is often impossible," he said.