On Thursday a report on the F-Secure Web site claimed the "first Vista virus" had been found.
According to the posting, an Austrian virus writer had published five proof-of-concept viruses that, in theory, could target Microsofts scripting shell, code-named Monad, and also known as "MSH."
But Monad is not expected to be part of Vista when it ships and was not included in the Vista Beta 1 bits distributed by the company late last month.
"These potential viruses do not affect Windows Vista or any other version of Windows if Monad has not been installed on the system. We have not yet announced a specific delivery vehicle for "Monad" in the Microsoft Windows operating system," said a spokeswoman for Microsofts security team.
"At this time, these reports pose no risk for Microsoft customers," the spokeswoman added. "The techniques described in these reports require the user to first load and run malicious software on their computer. The viruses do not attempt to exploit a software vulnerability and do not encompass a new method of attack."
Until fairly recently, Microsoft was widely expected to make Monad part of the next version of Windows. But Microsoft decided earlier this year not to include Monad in either the Windows Vista client, due to ship in 2006, or Longhorn Server, due to ship in 2007. Microsoft officials have not elaborated on the reasons for the decision to cut Monad from the next releases of Windows.