Something taking 100% CPU on windows

Some fragmented windows-related notes (mostly admin stuff)

TODO: Cleanup

Various windows services are known to be buggy and, under certain circumstances, take all CPU for little to no good reason.

To diagnose, run the windows task manager (Ctrl-Alt-Del) or Process Explorer (the latter shows more description of otherwise cryptic process names) to see whether there are any other processes constantly using CPU.

You can try quitting some system-tray applications the usual way (or via task makanger or process explorer) to see if you can tell whether something it doing this.

Note: This page does not address inefficiently coded/accessed things (soft modems, stupid/lazy drivers, some uses of parallel ports)

Antimalware Service Executable taking all CPU

This seems to scan all accessed files, so if this is consistently taking a lot of CPU, chances are something is opening a lot of files.

For example search indexing doing a reindex.

lsass.exe taking all CPU

Assuming you've checked for viruses and spyware (because there are a few that infect lsass.exe specifically)...

lsass.exe is the Local Security Authentication Server, and is used in many networked situations, handling local logon(verify) and various other security/authentication details, such as SSL connections (verify).

On desktop windowses, lsass is sort of a relic from its NT pedigree and is rarely doing much beyond helping secure connections.

Bugs in applications (or theoretically even just a lot of load from one) could cause lsass to take a lot of CPU. Things like VPN, VOIP, some chat programs, a webcam proxy application, and such. (In my case, a buggy logitech webcam service caused the problem - one of the few processes related to it frequently went crazy with requests on lsass. These processes could only be seen and killed in the process list)

On server-edition windowses, lsass may be doing more, e.g. handling domain logins, so this might be less of an issue in that it might just be handling a lot of authentication requests (because of, say, an inefficient LDAP server or so). If so, the high usage is a fact of current software -- but if it's consistently at 100% you might want to debug that, and/or upgrade hardware. In some cases the high usage may be a known and resolved bug which can be solved with an update or service pack.

HelpSvc.exe taking all CPU

A bug in the 'Help and Support' service caused it to use all CPU for a few minutes and possibly longer.

There is a hotfix for this, which was also included in at least XP's SP2, and probably others.

An alternative would be to have windows not start the service (set the service to be to manually started, or disabled.)

SvcHost.exe taking all CPU

Various causes, including....

Windows update

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Windows update may fail to start up, and take 100% CPU in the process (continuously, or for a few minutes each time it checks).

Diagnosis: If running net stop wuauserv stops the CPU use, this is your problem.

A temporary fix is to disable the service (Right-click My Computer → Management → Services and Applications → Services → )

A better one, if it works, is the correct hotfix for your problem.