malicious software removal tool

Every month, around the 15th, my profile settings are corrupted and I have to
do a system restore to get them back. The system generated restore point
immediately before this happens is labelled by the system 'Software
Distribution Service 3.0'. On looking into this it seems that at some point I
have accepted an EULA to download and run something called Malicious Software
Reporting Tool, and recently (a few months ago) Microsoft announced that they
would update this program each month (the second Tuesday of the month) and it
would from then on automatically run a system check in the background for
malicious software. I checked on Google and there was one reference to this
potentially corrupting profile settings for users.
This would seem to be the cause of the problem therefore.
The solution on the Microsoft web page was to remove tool from the automatic
updates list, however this item is not listed on my automatic updates (its
not hidden either). I have therefore changed my updates to notify me but not
download or install. When the program popped up a few days ago I did not
therefore download it. Yesterday however I did download a Windows Defender
security update (which I assumed was unrelated), however the system has now
been corrupted again.

Things I have done to try and fix this

1. Tried to remove it using add remove programs - it won't let you.
2. searched for the individual files in the directory to manually delete
them - they seemed to be system files and it wouldn't let me
3. I found a reference to this tool working in conjunction with Windows
Genuine Advantage, so I tried to remove that aswell as in 1 and 2 above - I
did find some files but couldn't delete the main one.
4. did a registry search to try and find these files and deleted a few
entries to at least cause the program to fall over (I hoped), but evidently
that didn't work either.
5. checked my firewall (zone alarm) and blocked the malicious software tool
- no effect (couldn't find Software Distribution Service in ZA so couldn't
block that)
6. tried to find either program in the applications tray to disable it
there (control alt delete) but couldn't see it
7. tried to block it in Windows Defender (in the bit that lists all programs
running) but its not listed
8. contacted Microsoft help on email who were totally useless
9. tried to access their expert user (I assume a blog page) but the system
kept telling me my settings weren't right to access that service. I changed
the settings exactly as they suggested but I still kept getting that message
10. in desperation rang them to enquire about paid support but they told me
they would charge £60 (even if it were a 2 minute job!). I am not prepared
to pay that for what is after all a Microsoft's bug !

The only other thing I can think of to do is to not download any updates for
Windows Defender either - assuming the 2 products are related. However I
won't know the outcome of that for another month since it only happens once a
If it is still causing a problem then I can only assume that the software is
already installed and will run once a month anyway without an update. If
that's the case I need to know how to get into the system files to disable it
- surely there must be a way ??

Any help you can think of to give me would be very much appreciated - I am
certainly trying to fix it myself without asking anyone and have spent many
hours doing so, but I am at a dead end!

For info I am running Windows XP Home, SP3, with AVG and ZA.

Many thanks for your help.