I've been using Comodo's free Internet Security Suite for a couple of years and I have not had any problems with it. However, when I recently bought a couple of new notebooks for the new office and tried installing it, I realized how inefficient it was. The Comodo installer itself is about 80MB in size and you can download it from Comodo's site or at CNet. The problem is Comodo does not provide a site where you can download the latest virus signatures as a single file. You have to download it using the Comodo software itself.
The anti-virus database (CAV file) from a fresh install is so large (about 129MB). The download process keeps failing due to time out. Comodo does not seem to have a partial download/update or a resumable download capability. If the entire download does not work, the whole thing aborts. Also, if you have several PC's or notebooks, you have to download that same file on each PC. It would be so much more efficient to just download a single large database update file and install it on each individual PC's.
Reading through several forums, I found out that there is an unofficial way of doing this. One can copy the scanners subfolder (specifically, the bases.cav file) of an up-to-date installation under the c:\program files\COMODO\Comodo Internet Security folder to the new PC. But since its a special folder, you have to switch to Windows safe mode first (http://www.pchell.com/support/safemode.shtml) before you can overwrite your copy. I tried it and it worked!