Hi do apps such as battery doctor and cm security work?

[Wayne Ali]

Can they be harmful?

 

[Golfdriver97]

Welcome to the forums.

Battery doctor might more detrimental. Android already does a pretty good job at task management. If you have something draining your battery, there are many other, and easily better, options on Play.

For me, CleanMaster started asking for excessive permissions that I didn't care for, so I stopped using it.

 

[Rukbat]

Unless you're running Android 2.0 or earlier, any task killer app should be avoided like the plague. It wastes battery and slows the phone down. In most cases it kills tasks that Android need, so Android reloads them, only to have the task killer kill them again, only to have Android load them again, etc., etc.

Read Multitasking the Android Way The author is an Android software engineer (one of the people who develop Android), so she should know what she's talking about.