Doesn't work for me. I just installed an update right now. The last definition update I had was created at 5am this morning. Since then a new update came out at 1pm that the program didn't fetch. I had to once again update manually. Microsoft may indeed be updating the definitions 3 times a day, but for me it isn't automatic. The whole point of an effective anti-virus is to get the new signature file as soon as it's released, not a day after.