Easy Fixes for Slow Computers: 2. Run an adequate anti-malware program (and keep it running).
It’s critical to use the right software to detect malware, clean it out, and prevent future infestations. I suggest AVG (although truth be told that company is starting to get on my nerves). Their free anti-malware program is very good and will not cause further problems to your system (like Norton, which I hate).
It’s up to you, but you really do not need to spend any money on anti-malware. The AVG version is completely free and suitable for home computers.