As per the source(www.cio.in), Microsoft has confirmed first bug with Windows 7. A Canadian researcher, Mr. Laurent Gaffie is the first person who reported this bug. As per Gaffie’s blog entry, this bug triggers a infinite loop which can make the windows 7 system unusable. This bug can be triggered via SMB or through IE.
One can read about this bug and the advisory at Gaffie’s Blog