When I run CCleaner, it somehow gets lost and just runs and runs. Even when left overnight, it will still be running the next day.
I finally tracked this down to the step under "Internet Explorer" called "Temporary Internet Files" by trial and error. I started by unchecking everything except "Empty Recycle Bin" and then using the "Analyze" and "Run Cleaner". Then I checked one at a time until I found the step that was causing problems. Whether it is the only one checked, or everything is checked, the "Temporary Internet Files" step causes this problem. Even manually cleaning this directory (including hidden files) did not make the problem go away.
Using the Task Manager to kill the program causes the window to close, but the process continues to take most of the CPU cycles. Killing the process or the process tree doesn't make the process stop. The only way to get rid of the process is to shut down the system. Sometimes that requires a hard power off.
I used the SysInternals File Monitor and Process Explorer to investigate. Both seem to confirm that after CCleaner scans the "Temporary Internet Files" directory, it starts opening the C: root over and over. It appears that it is in an endless loop at that point.
The computer is running Windows XP SvcPk 2 and is fully patched.
(Lets see, did I miss anything important? )