The background to this posting can be found here: http://community.norton.com/t5/Norton-Internet-Security-Norton/Idle-Full-System-Scan-Off/m-p/614694/highlight/false#M187128
However, as the above thread evolved into an off-topic discussion on memory/performance issues with Crypt32.dll, I restate my own findings here. Briefly, to rectify a Crypt32.dll memory leak on my XP/Sp3 box, I uninstalled KB2641690 and then reinstalled the same hotfix with the /B:SP3QFE switch. The 'run' command used was: WindowsXP-KB2641690-x86-ENU.exe /B:SP3QFE
After reinstallation, Crypt32.dll properties confirmed that the QFE branch had been installed. Version: 5.131.2600.6154 (xpsp_sp3_qfe.110927-1620). Total Commit Charge (shortly after boot) was around 290mb, as it should be, rather than 430mb. If this holds, and that's a big IF, maybe the solution to my (XP/Sp3) memory problems.
More on Crypt32.dll and the 2 branches of development for updates, GDR (General Distribution Releases) and QFE (Quick Fix Engineering), here: http://social.technet.microsoft.com/Forums/en-US/itproxpsp/thread/c11530e8-56e2-4bb3-a887-f7809e644861
Best, CBA