One of my clients at work was also a victim of the latest McAfee false-positive trouble. In case you don't know what I'm talking about, read the official statement (and remedy): https://kc.mcafee.com/corporate/index?id=KB68780&page=content.
Basically the issue is that McAfee wipes svchost.exe from your system because it thinks there's a virus in it. And this file is in fact quite critical for Windows to function properly.

My client managed to skip by the worst part of the trouble, and only had this issue on two of their desktop computers (running Windows XP SP3). Their systems were not entirely crippled as they would still boot and log in, but they were otherwise unable to use networking, s  ...