Avast antivirus causing crashes in games?

Are you sure it is Avast causing the crash and not the X1950 Pro or even your PSU?

Avast used to crash some of my games when it would 'notify' me of actions it performed, such as definition updates. This would happen on a few of the computers in my house.
Try disabling notifications by going to Program Settings->Confirmations and uncheck all of the boxes.
I still have to ask, though, why you deduced that Avast is the culprit? Many things could cause a game to crash.

Well I used to have Norton Antivirus, but that seemed to be slowing down my system as well as causing a 'looping sound crash' with Steam games (especially hl2). So I uninstalled Norton and got a speedier computer, albeit one that was vulnerable to any virus out there. And Steam worked perfectly. It definitely cured that looping sound crash which has baffled huge numbers of people. However, Steam do say in their tech support docs that you should always run steam without any antivirus software! Which I think is a bit difficult for people to do.

Anyway, that got me paranoid about antivirus software and steam. And lo and behold, I installed avast and now I'm getting crashes again! Apart from Oblivion, most of my other games work fine. And yet some people seem to run steam ok with antivirus software installed, so I am totally confused! I will try disabling the notifications in case that is causing a problem. I just wondered which AV people use in conjunction with Steam, without any problems?
;xmrb2003x@

Like Cybercatter not, Steam makes that suggestion only because Virus apps love to hit you with a Virus definitions update pop up right in the middle of your favorite games so they recommend you disable them prior to playing.

Kaspersky is a very good, low profile (doesn't use much system resources) anti-virus app. And disabling it and Turning off notifications is really simple.

I see, but is that the only reason though for valve to say that or is there a more fundamental clash with the running of the code (i.e. does the antivirus think that steam is a virus and try to stop it running?). My crash to desktop doesn't seem to coincide with the pop-up auto update thing, it just seems random. But I have changed the frequency of the update to less frequent anyway, I'll see if that helps.

Thanks and can I assume you are running Kaspersky with Steam and no problems?
xmrb2003x@

If it helps you, I run Avast all day without it crashing my machine. I don't disable it when running games (although it is a bit disconcerting having a booming American voice tell me the virus database has been updated during a DAO cutscene). It also doesn't appear to have a problem with Steam.
I'm running Windows 7 on a Q6600, so I wonder if the multitasking has an effect on this. Are you also sure the CTD isn't anything to do with the fact that your pc is struggling a little with the games involved?

An edit on my post there, the newer version has a checkbox just for gaming. Its in
Program Settings->Troubleshooting: 'Check for full screen applications(e.g. games) before displaying popups' box.

I've used Kaspersky as well, and like TheViper said, its not bloated.
I've also heard that Norton 2009 Gaming Edition is supposed to be resource friendly, but I haven't personally tried it.

Aha, I read somewhere that you have to stop the "ashdisp.exe" process AFTER disabling the self-defence module. That seems to have done the trick! I also have a 2nd monitor with an extended display, so I had to disable that from the display properties (and select unattach for the 2nd monitor). That seems to have fixed tearing on screen, and boosted performance too. Can't believe I'm playing HL2 episode 2 with no crashes at last (so far anyway)! Maybe I can finish it after all lol!

Oblivion still has the odd crash, but is running a bit better. I'll see how that goes. Thx

Hmmm avast was giving a problem to me as well

I love my avast but it kills my games. It still wont let me play anything by Lucas Arts unless I turn it off. Turn it off and try to avoid any questionably web pages while it's off.