I'll have to apologize in advance for the very limited information I have. The computer is not mine, the person who asked me to look at it didn't provide a whole lot of detail, and has taken steps on her own which seem to have eliminated the worst of the symptoms leaving me unable to observe them for myself or report on them in any kind of detail.
Let's start with what I was told. After visiting a web site containing some racy material, the computer started popping up messages threatening some kind of harm (not sure exactly what, file deletion I suspect) if the owner didn't pay someone money. I was also told that the camera on the computer was observed to have been activated when it should not have been, presumably by the suspected infection. I was asked if I would take a look if they shipped me the computer, and I said OK.
So the computer was shipped, but before sending it the owner tried using Norton Security Suite (apparently a full version provided at no cost by the owner's ISP, Comcast) which seemed to eliminate the infection, but now the computer was running very slowly.
Once I got the computer, I was able to determine that the performance problem was caused by Norton's AutoProtect module repeatedly finding and "dealing with" a vulnerability called "Suspicious.Cloud.7.EP" in file C:\users\<username>\appdata\local\intel\dmzbsycu.dll. The action taken by Norton in "dealing with" the vulnerability was listed as "No fix attempted", so the vulnerability remained, and Norton kept detecting it and "dealing with" it by not doing anything, repeatedly and constantly, consuming all the CPU cycles.
I was able to get the computer into a usable state by disabling AutoProtect temporarily. I tried a couple of other scanners, and one of them (McAfee Stinger - I used the portable edition from PortableApps.com) was able to actually remove this file, after which Norton seems to be happy. Having accomplished this, I tried looking back through Norton's logs to see if I could figure out what it might have fixed or removed, but they onliy go back a few days (probably because it's filled with the "Suspicious.Cloud.7.EP" detection events), which is after the owner's attempt to remove the virus herself, so I can't even tell what Norton did to eliminate the symptoms.
So as of right now, there are no active problems that I can detect. But since I won't have access to the computer anymore once I send it home, I hope to get it as clean and well-protected as possible.
To that end - is there any chance someone would recommend and look at some scans to help me make sure everything is ship shape? And do you have any recommendations on security software? I've had problems with Norton in the past, and my experience here seems to indicate that it can still be a troublemaker, particularly for the novice user. Is there a better choice? I myself use Microsoft's free Security Essentials (on the advice of someone here a while back, actually), and it's worked well - and very transparently - for me. And transparency is pretty key for this particular user - the more automatic, the better. For example, the owner is not someone who would ever have figured out on her own that she needed to disable Norton just to be able to use the computer, and then remove the virus through other means. Thanks for any help and/or advice you can offer.