Steam News has word that a new patch for Left 4 Dead 2 is now automatically available. This is a hotfix to close off an exploit, as word is: "Fixed original survivors cheating in Bleed Out mode by throwing first aid kits." What's Bleed out mode you ask? The Left 4 Dead Blog explains, while also revealing the "talking" Boomer plushy is now available in the Valve Store. Here's word on Bleed Out:

New Mutation
Bleed Out
Your health is a ticking away! With constant mobs chasing you, there's no time for standing around. You have no permanent health, only temporary health that is continuously ticking away. You won't find any health packs to restore your health, only pills and adrenaline. This mutation is for Campaign mode.

Remember, each week a new mutation will be coming out, so you need to check back every week.