Currently there is an update for steam whenever i try to update it steam gets to 99% and then it says that it detects 2 malware viruses and doesn’t let me play them,
[Chest] C:\Program Files (x86)\Steam\sdl.dll
WIN32:malware-gen
Moved to chest
C:\Program Files (x86)\Steam\Steam.exe
[Chest] C:\Program Files (x86)\Steam\bin\sdl.dll
WIN32:malware-gen
Moved to chest
C:\Program Files (x86)\Steam\Steam.exe
Same files are affected for me starting today, I reported false positives using the Avast! User Interface, registered on the forums to see if others suffered from the same problem and saw this post.
You aren’t alone! Glad I’m not either. I can do with a day or two without playing Counter-Strike:Source though, I suppose it’s Christmas anyway. 
OS: Win 7 Professional 64-bit
Avast Version: 7.0.1474 - 12/24/2012 8:47:34 AM definitions - 121224-2
EDIT: To ease my mind I submitted to virustotal, results look good, with only Avast! detecting it as malicious, looks like it’s a false positive.
You have done well. Just be patiently and wait till this false positive will be corrected by an streaming update.
DJBone