How to detect:
1. Check resource allocation using task manager. Identify any unknown program using high resources. It's a manual process.
2. Buy a licensed version of nternet security package which contains anti virus, anti malware/spyware and live internet usage. It's automated and easy. Don't rely on free to download antivirus softwares

How to protect:
1. Check point no 2 above.
2. Don't download random softwares from the web.
3. Strictly don't use any torrent related websites

I think you will do just great if you follow these instructions.