Do not trust the free software tools offered by unpopular websites which will harm your computer. If you install the free software it will automatically installs the spyware programs automatically without your knowledge. Spywares will watch the websites you visit and steal your personal information and share the information with all spammers.
Particularly if you try to download any software using Torrent/Torrent downloads you are more vulnerable to all software threats. This may harm your hardware as well as BIOS in your system.
Apart from the above there is one more possibility of threat which will harm your operating system. The operating system gets corrupted when the systems files fail to run automatically. The free software would have shared the system files while installing its initiation information to run. When you uninstall the software it may delete some shared files which would have used by your operating system.
Please take extreme care when you download free software from internet.