Previous AV on my machine was AVG 7.5 followed briefly by 8.0 plus Spybot plus Ad-aware 2007. Removed AVG via add/remove in the control panel, and made sure the Grisoft and AVG folders in Program Files and Documents and Settings are no longer there. Any other steps in making sure it's all gone?
After installing avast I ran the boot-time scan, which found a few generics in the System Volume Information restore directories but nothing in the Windows directory. Subsequent scan show up nothing.
When I first noticed the problem, I still had Ad-aware 2007 and Spybot 1.5.2 plus Spybot-SD Resident on my system along with avast! 4.8.1201. I've removed Ad-aware (via their uninstall shortcut?), and am now running Spybot and its Resident at version 1.6, SUPERAntiSpyware Free and Malwarebytes' Anti-malware. No firewall running on the machine (running one at the gateway).
With avast, I'm now running 4.8.1218 Home with the default providers and have not made any changes other then (i) disabled skins, (ii) show results of Explorer Extension scans and (ii) check for full-screen applications before showing pop-ups (as I run quite a number of games).
I tend to notice the problem after I've been gaming for a while e.g. over the past few weeks I've been running Guild Wars plus Ventrilo plus Ventrilo server running for a few hours - Guild Wars and the Ventrilo programs continue to operate fine to the internet, but the web browsers cannot retrieve anything. It's also occurred at other times though - on a couple of occasions where I've run iTunes shortly after boot-up I've noticed that it was not downloading my podcasts, and then that my email and web were not going either. When it occurs the indications are that all processes are running normally - ashWebSv.exe is not using CPU time, and no other programs or services are hogging resources.