Microsoft is warning about a new piece of malware, Rogue:MSIL/Zeven, that auto-detects a user's browser and then imitates the relevant malware warning pages from Internet Explorer, Firefox, or Chrome. The fake warning pages are very similar to the real thing; you have to look closely to realize they aren't the real thing. The ploy is a basic social engineering scheme, but in this case the malware authors are relying on the user's trust in their browser, a tactic that hasn't been seen before.
"Politeness costs nothing but gains everything".