Imagine this: you make a new (re-) installation of Windows XP on some old PC you want to make good use of. You add all the updates, day after tedious day of updates. You do the whole Genuine Advantage thing. Everything seems to work fine. You install Microsoft Security Essentials (from a memory stick) so that the nasty red messages go away, and go online.
And then performance goes down the tubes. One of two processes MsMpEng.exe or msesec.exe is hogging 54, 72 or even 98 percent of the CPU. And it does it even when the network is disconnected.
In what universe does a computer need antivirus protection that consumes nearly 100% of CPU when the system is not connected and when the user is not making any changes? A cynical person might think Is Microsoft deliberately knobbling older installations of XP in order to force people to upgrade to Windows 7?, perhaps with guilty pleasure. This is not the result of some disc scan, nor is the result of having to anti-virus systems going at the same time: Microsoft's anti-virus system is itself acting like a virus.
Looking through the Internet, it is clear that this has been an issue reported multiple times over the last year. There is a very nice fix up from Microsoft support from Feb 2010 on PC World:
1. Open Microsoft Security Essential program. 2. Click settings tab 3. Excluded files and Locations 4. Click on Add button. 5.Select the path c:\program files\microsoft security essentials\MsMpEng.exe 6. Click ok. 7. Click on Save changes. 8. Close Microsoft Security Essential program. 9. Restart the computer.
(Guess what: it doesn't work for me. I see other advise on the WWW is that there may be "conflicts" with other services. Conflicts? WTF....)
The problem, believe it or not, seems to be that the anti-virus program is continually checking itself. So you have to tell it to exempt itself. Boy.
Now I wonder whether the problem came up because I was installing Windows Security offline: the first thing it tries to do is update itself. Microsoft has had a fix for this for at least six months. Why haven't they fixed it? I don't recall seeing any warning that you cannot install it off-line, for example: if the problem is just that (is it?) would it have hurt to mention it?
I tried all the combinations of switching on or off options, rebooting carefully each time. Nada. I even tried searching for where the Security Essentials could be storing its data, but of course the new Search that installed itself (I don't recall OKint it) from Microsoft update won't work: it claims the disk is not indexed when I try to do a search, but when I try to index the disk it does nothing, saying the disk has been indexed. I will need to see about uninstalling that new search.
What worked for me in the end? I have uninstalled Security Essentials. I'll go back to keeping that machine offline as much as possible and running Malwarebytes after each online session (and use Thunderbird and Firefox instead of IE and Outlook when they are online, etc.) I was recently thinking that my move to PC-BSD on my main PC has been less smooth than I wanted, but it is nothing like this rubbish.