If you get kicked by Punkbuster for corrupted packet flow and run Microsoft Security Essentials, try to turn of the real-time protection in MSE.
This problem suddenly started for me yesterday, and I got kicked on every server - until I turned of the real-time protection.
Never had problems with MSE before, so must be something in the latest update.
Today I see a lot of other players that seems to have the same problem around on servers, so hope this tip will help.