High Steam cpu usage

[Syobon]

Steam use a huge amount of CPU while playing civ in multiplayer mode is this common? it eats up to 25% here, in process hacker i identify the tier0_s.dll as the culprit.

here what happens
http://i.imgur.com/GPzhk.png

 

[greygamer]

This seems to be a process used by STEAM. There have been some issues with people who run AVAST which detects this file as a virus.
The file/process seems to be at the heart of how STEAM operates, if it is blocked/disabled then STEAM doesn't work.

Someone more knowledgeable about STEAM's software can probably explain why it is such a resource hog