My computer recently started asking to be reauthorized

Question

My computer hasn't changed since I started using iTunes 2 years ago.
Over the course of 2010 I bought the first 6 Harry Potter movies (for my daugther) on bluray with Digital copy and downloaded them via iTunes.
All hasn't been a problem.  I gave her the remaining 2 (Book 7 parts 1 & 2) for Christmas.
On 1/2/2012 I started downloading them both.
After they finished I also got the latest iTunes update.
I shut down that night.
The next day iTunes made me reauthorize the computer and it treated it as a different computer (i.e. it said I now have 2 authorized computers).
Tonight on 1/13/2012 it did it again, and now says I have 3 authorized computers!
If this keeps up soon I'll have to do the "Deauthorize All Computers" thing in my iTunes account, since obviously I can't deauthorize the "current" computer and expect it to remove them all even though they are the same exact machine!
That would just be a PITA, except when I looked up how to do that, it said you can only do that once a year.
I'm worried that it might keep doing this and in a month or two I'll be completely unable to use iTunes for my DRM'd content.
I'd like to head this off before it becomes a big problem.
I'm on iTunes 10.5.2.11
FYI, I don't think this matters but:
I have a old iPod Nano 3G which is currently loaded with a bunch of audiobooks from Librivox, and one from iTunes which is DRM'd.  But otherwise I rarely connect it to the machine because it takes me a long time to listen to 8G of audio books (I load it up, listen to them all, then delete 'em and load a bunch more).
One other thing, after 1/2 and before 1/13 (i.e. between the 2 reauthorizations) I signed up for Audible and downloaded a big audiobook.
Also, I don't currently have any music in iTunes, just audiobooks and movies.

Answer 1

Do a malware check with some malware scanning programs on the Windows computer.<br />
You need to scan with all programs because each program detects different malware.<br />
Make sure that you update each program to get the latest version of their databases before doing a scan.<br /><br />
*http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware
*http://www.superantispyware.com/ - SuperAntispyware
*http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page
*http://www.safer-networking.org/en/index.html - Spybot Search & Destroy
*http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free
See also:
*"Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked