Well besides running an anti-virus, Adware or Malware software to check and confirm you do have one or all. The other most common way is that if your computer or laptop is starting to run funny or. If it shuts down for no apparent reason It locks up on you when you are doing nothing You can't find a file or two Some programs don't run properly or they way they used to run. Your computer or laptop is extremely slow compaired to when it was new. Then odds are you might have been infected with a Virus, Malware, Adware or Trojan.