A WebmasterWorld thread has a few users complaining that every time they login to Google Webmaster Tools, they are prompted with a security warning by their browser. The warning is similar to this:
Supposedly, it is not just Google Webmaster Tools. One member complains it has to do with AdSense's console as well.
I can tell you that I rarely personally get this warning and it might just be the nature of the user's browser. There is no official word from a Google representative on this matter, at the time I publish this piece.
Forum discussion at WebmasterWorld.