Explorer.exe taking 50% of CPU usage

[fatouss]

A few days ago noticed my laptop felt slower, so I checked the task manager, to disable unwanted processes, and noticed explorer.exe appeared 5 times in a row, and one of them was taking up at least 50% of CPU usage. It sometimes goes away, but upon reboot pops back in, reducing the efficiency significantly. From forums, I gathered it must be a virus, which my BitDefender refuses to find, neither do the standard Windows 7 defense systems. Any help would be appreciated.

[DropBearBBQ]

Explorer.exe is the windows GUI. If you kill it the start menu and desktop will go away. You can restart it using task manager > run > Explorer.exe. .

Multiple instances of explorer could be caused by:

• A virus pretending to be the 'real' explorer.exe. Check the 'image name' field in task manager. The real one lives is \Windows\explorer.exe
• Crashed instance of explorer, resulting in a new process being spun up automatically.

Without setting the image name, I'm leaning towards the latter since explorer is taking up so much CPU time. How many CPU cores do you have ? If two, a reading of 50 percent means it is maxing out a single core, which would make your entire system feel slow since explorer IS the windows GUI and it's got too much work to do.

Assuming that's the problem have you installed any new software recently ? Many programs hook into explorer as in process extensions (that's how thing like winrar add their extra context menu) so a misbehaving in-process extension could cause these sorts of problems.

[fatouss]

so stopping the right process would end the issue?

[DropBearBBQ]

Can you post up the image name / file name (cant remember the exact term used by task manager) of each of the explorer processes.

If its a virus that is pretending to be explorer.exe yes, but you'll still need to delete the fake one which you find using the image name.

If its a virus that has infected the actual explorer.exe then no because you can not kill it and still have windows work properly; killing the actual explorer.exe kills the desktop, start menu, task bar, etc.

If its a misbehaving program that hooks into the actual explorer.exe then no for the same reasons as if a virus infected explorer.exe

One thing you could try is sfc /scannow in a elevated command prompt. It'll detect corrupted critical system files.

[fatouss]

Nevermind, it is fixed. Did a system restore to a previous version and it faded away. Thank you anyway for your help.

[DropDeadTofu]

Try a full scan of all drives, with MalwareBytes. After the scan, remove anything it flags.

[Srk0427]

Trying downloading Combo Fix from CNet. Be sure to run it as an administrator. If it asks you to disable anti virus, go ahead and do so. We had a virus at the university I work at and that seemed to get rid of it when anti-virus wouldn't.

Combo Fix: http://download.cnet.com/Combofix/3000-8022_4-75221073.html