This bug can be founded when before latest update you installed Flash Player from Adobe and after that update you Mac OS X.

Bug symptoms

• Fan always run on high speed
• OS really slow
• In System Monitor (with all processes flag) you can view process with PID 0 and name kernel_task that use to much CPU time (ex.: on Air mid 2013 - ~300% of CPU)

Bug fix

If you find a solution with deleting something from one of *.kext dir - don't use it! This can crash your system. More appropriate solution is reset SMC and PRAM.

SMC reset

1. Unplug the computer's power cord for 10-15 minutes
2. Shut down the computer
3. Attach the computer's power cord
4. Press and hold the Shift+Ctrl+Option+Power combo for 10 seconds
5. Release the combo, MagSafe led can change status for 1-2 seconds
6. Power on computer

PRAM reset

1. Shut down the computer
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.