Unwanted Apps (Maybe malware) downloaded and installed on Android device

This is some kind of virus that has worked its way into the operating system. The only solution is to flash the default operating system again.

Since you did not specify the phone model, I'll be generic about my answer.

Reflashing the stock operating system is a process where you download the default operating system from the phone manufacturer website and load it into the phone, overwriting the existing operating system which is infected. A factory reset will not work in this case. Doing this involves unlocking the bootloader, which will void the warranty. Contact your phone's manufacturer and ask if there is a way to repair the phone without voiding the warranty. If there isn't, google your device name and "flash a custom ROM", or a custom operating system that many Android professionals prefer over the stock one. In your case, instead of writing the alternate operating system, we are simply rewriting the default one from the manufacturer.

I think some malicious process running on your device so go to

Settings->App->Running (Tab)

and try to identify unwanted process and if you get it stop the process and try to uninstall belonging application of respective process.