The antivirus market is, as everyone knows, the most FUD-filled part of the security industry. The effectiveness of different antivirus products is largely anecdotal, and shifts rapidly because of the arms race between virus writers and antivirus manufacturers. As it stands now, even "expert" end user cannot ascertain the relative effectiveness of the suites, and because antivirus products are still heuristics-based with a few "depacker" routines built in, they only catch the really obvious fish. (One funny thing with this is, if you pack an executable with a common yet relatively complicated packer, say "redeye", it'l get caught, but if you just jump in and jumble up the instructions with a debugger you can make it "invisible" easily). Because of this reliance on FUD to sell, and because there *is* already fierce competition in the antivirus market, maybe this won't change much, unless MS locks other vendors out somehow. Or will it be a different form of competition, because of the now-asymmetrical playing field? MS has an advantage in that they have access to the code and people who wrote the code, and designed the OS architecture.