Wow, a lot of hostility in this thread.
I was just scanning the forum looking for any repetitive negative issues that users are experiencing using Avast (hard to believe, as some give the impression Avast is perfect right here in this very thread!), when I stumbled upon this relatively outdated yet purposeful thread. One reason why you'd want to CLOSE an AV is when installing drivers. Disabling is probably good enough, but I go the extra mile and prevent it from running during video driver installation. I regularly update video drivers that may benefit my system to some degree, as I'm an avid gamer (have been since the late 80s) and it's definitely worth the extra minute or two after downloading the driver to disable ALL extra programs that run on startup, especially the 'unnecessary' ones, for the duration of the simple driver installation process. Programs such as Steam or Xfire, (there are built-in options in those to prevent running at startup, uncheck those boxes), and yes, your ANTIVIRUS program. Horrifying isn't it? I know, I'm a moron to do so, what possible reason would I have to do so? It's pure insanity! It's actually common sense. Also, disable the internet connection, (you can't get a virus if you're isolated...I'm not sure if those terrified at the mere thought of closing their AV know this, so I thought I'd play Captain Obvious for a second here, quite a bit of sarcasm here, more than usual anyway)...in my case, unplug the cable, if you're wireless, obviously you'd disable your adapter before rebooting. Shouldn't need to mention this, but I'll do it anyway; you will have already scanned the downloaded driver files, automatically I hope, (but hell, I manually scan them even though I've set my AV to do so automatically) before doing this, so having it running during installation is unnecessary.
Now, you may think this is extreme, or overkill, even unnecessary, and it probably is, but as I've had practically zero issues running any game on any of my systems, past and present, using these quick and simple precautions; (sans general debilitating issues that developers claim responsibility for and with any luck release a patch fixing such issues). But we're talking user error here, as in incorrect installations and/or settings or even poor hardware...piss poor power supplies, anyone?) I can simply skip the few aforementioned steps, install the drivers with AV simply disabled, then troubleshoot for hours in the event something may go wrong. Yes, I'll admit, it's a big IF, but I'll just do it 'right' the first time and avoid chancing that remotely possible 'IF'. Especially since driver updates are relatively infrequent, and it's just a few minutes of one's time to install them properly. So, yes, I'll continue using this procedure which includes having the AV CLOSED during installation.
I also admit I play too many games, I have ~700 on Steam alone and that's just one of many sources I purchase games from. If you've read any gaming forum, you'd see thousands, if not millions from over the years, of users with various game related isssues, many of which are video related, subsequently due to a driver issue. Whether it be because of an incorrect version, improper installation, inappropriately adjusted settings via utility program, or simply inadequate hardware. Correct installation is the first step to narrowing the troubleshooting procedure. Or maybe I don't know what I'm talking about, so just download and install, it'll work just fine, Windows knows what it's doing, if there's a problem afterward, it HAS to be the company that made the program that's now not working as it should, or your hardware vendor, they haven't a clue what they're doing, do they? I mean, it couldn't possibly be user error. Many of those problems in the forums can be attributed to improper driver installation. I love the 'don't buy this game because it won't run on my particular system' threads. My money's on incorrect installation and/or improper settings (whether it be bios, utility programs, overclocking, etc), or simply inadequate hardware specs (e.g laptops with very cheap video).
The point being, his question was legitimate, the crass remarks were unnecessary, ignorant even. Sure, having the AV disabled or even just leaving it running probably won't ever corrupt a driver installation for most people, especially non-gamers, as they're less likely to update critical hardware drivers, namely the video, but why take the chance? It takes less than half the time to do it right than it took me to explain one of only two, maybe three reasons you'd actually want to terminate an AV program, if ever. Basic third grade material.
Yeah, I registered just to state the obvious. Perhaps if people did stuff right, we wouldn't have to fix what shouldn't have been broken in the first place. Judging from this thread, that's not going to happen anytime soon.