What program hides in a computer and allows someone from a remote location take full control of the computer?

Its called a R.A.T which is Remote Access Tool. These programs are encrypted allowing them to pass unrecognized through Anti Virus software. AV companies are constantly updating their software as hackers find new and better ways to stay undetected whilst in your computer.

These programs are illegal if used to enter someone's computer without their knowledge or permisson.