A backdoor is a silent way into your computer via websites, software, or OSes. It is achieved by exploiting a vulnerability in one of them to get in and control your computer without your consent. Many backdoors (and related security holes) can be found in outdated versions of software.
Problems backdoors can cause
Backdoors compromise the safety of anything related to your computer. They can launch botnets which silently run on your computer without your knowledge, illegally.
Protect yourself from backdoors
- Update your software and hardware.
- Do not use unlicensed software.