A while back I wrote about a free for corporate use antivirus solution called Immunet. The cool thing about it is that it has the tried and true ClamAV engine built into it for offline protect when not connected to the Internet. Plus it give ClamAV the power of on-access scanning which is something that ClamWIN does not have.
The problem with Immunet though, despite their claims, is that it is kind of a resource hog. We put it on our user's computers at work for a while, but then we received a lot of complaints about performance issues.
There is a really simple solution though. You see, by default Immunet has two cloud detection engines enabled. One is called Ethos, and the other is called Spero. These require your computer to be connected to the Internet, and they rely on the community to detect malware on your computer. The trick to speeding up Immunet is to disable the cloud detection engines and just leave ClamAV enabled. You can set this in the scan settings:
After doing disabling the cloud engines performance was greatly improved, and my machines were still protected from viruses with ClamAV.