Yesterday, I lost my access to the Internet on my main computer running Windows 7.
The tiny network logo in the bottom of the screen had an even tinier yellow warning triangle on it. A little fiddling with Windows' "Network and Sharing Center" and the Microsoft diagnostic tools concluded that my computer Cannot Access DNS Server.
OK. Reboot. Boot the router. Boot the DSL modem. No go.
Upstairs to the kitchen computer. Everything is cool. Try the iPad - cool there too! Only the hardwired computer has a problem. Blew an hour or more looking for a wiring problem.
It took me a while to find this post on the Tech Support Guy site. And this post at A Technical Journey. Yes indeed, McAfee caused this problem with a an update back in mid-August.
I, of course, don't install software updates until they have been out for a while so that the vendors can fix this kind of bug. I made the mistake of letting McAfee update itself two days ago, then rebooted yesterday to sever my Internet link! Wouldn't you think they might just delete updates that cause this?
As I have stated many times, I have had to fix far more problems caused by Antivirus software than by virus and malware.