......I've been using Avast with Steam for years. It's only been in the last few months that Steam started having issues with Avast.
......I know Avast had a program update sometime in the last few weeks. But I was still having the same problem even after the update.
The first problem that I encountered was this:
......Steam would start but the game that I selected would not start. I found out that the game was updating but there was nothing to indicate that that was what was happening. The usual update box and progress bar did not pop up, but I could see the update progress on the steam page.
......At this point I only had to turn off Avast real-time shields until the update was over and then the game would start and run normally.
But eventually the problem got worse.
......Left 4 Dead 2 wouldn't start or would load very slowly. Once in-game the screen would lock up for 10-30 seconds at a time at similar intervals.
......Killing Floor loaded very slowly, and glitched with poor frame rates and intermittent slow downs.
I swept my machine for viruses and root-kits.
I checked my video card and RAM for errors.
I reinstalled steam and my steam games.
I completely uninstalled and reinstalled Avast.
I tried shutting down one Avast shield and then another and so on.
I added the steam folder to the File shield exclusions as I noted below.
I set the heuristics settings in all shields to the lowest settings.
Nothing worked. I had to shut down all Avast real-time shields to play without the lock-ups.
......I was still having the same problems after the update but I decided to try again since there was an update. I went thru the shields again and put exclusions in wherever I could and it seems to have worked.
......I have listed my Avast settings and exclusions below. I hope it helps.
......If you're wondering about a setting that I have not noted here, it's set to default on my machine.
......I have not tried these exclusions one at a time or in any other combination to see if only one or two will do the trick.
Windows XP Home 32bit OS
My computer is a Dell with a 2.99ghz single core P4
4gb of RAM
with a Sapphire Radeon HD4870 Toxic Vid card
with Verizon FIOS internet
Avast
program version 6.0.1289
datbase version 11091801
last updated 2011-09-18
Open Avast user interface
go-to Real-Time shields
Find the appropriate entry below
____________________________________________________
File system shield - Expert settings - Exclusions:
add the steam folder to your exceptions (this alone doesn't stop the problem)
D:\program files\steam\
File system shield - Expert settings - Advanced
make sure all three are checked
Do not scan verified system DLL's
Use transient caching
Use persistent caching
File system shield - Expert settings - Actions
Select action to be performed when a "Virus/PUP/suspicious" is found:
set to ask under each tab
File system shield - Expert settings - Sensitivity
make sure sensitivity is set to normal
UN-check
Test whole files
Scan for potentially unwanted programs
____________________________________________________
Web Shield - Expert settings - Exclusions
make sure URL's to exclude is checked.
add
http://store.steampowered.com to "URL's to exclude"
Web Shield - Expert settings - Sensitivity
make sure sensitivity is set to normal
UN-check
Test whole files
Scan for potentially unwanted programs
____________________________________________________
Script Shield - Expert settings - Exclusions
make sure URL's to exclude is checked.
add
http://store.steampowered.com to "URL's to exclude"
____________________________________________________
Behavior Shield - Expert settings - Main settings
All three are checked
Monitor the system for low level root kits
Monitor the system for malware-like behavior
Monitor the system for unauthorized modifications
Action to take = ask
Behavior Shield - Expert settings - Trusted processes
add these exe's to the list
D:\program files\steam\steam.exe
D:\program files\steam\GameOverlayUI.exe
D:\program files\steam\steamerrorreporter.exe
Also add the .exe for any steam game that you may be having an issue with.
D:\program files\steam\common\left 4 dead 2\left4dead2.exe
D:\program files\steam\common\killing floor\System\killing floor.exe
.....As I said above, these setting seem to be working. I'm not getting freeze frames and my load times have improved. I hope this helps others whose problems weren't fixed in the latest Avast update.