Viruses are created by assholes looking to make easy money often by creating a file that people can download, normally disguised as something else. People think they are downloading one thing, but they get the virus instead. After this happens, it depends on the virus. The victim may not be able to access their information, their computer may be monitored by the hacker so they can learn the victim's passwords, some hackers even use other people's computers to commit serious crimes, so the virus victim appears guilty. It can be difficult to trace back where the hacker is. But most of the time, the creator of the virus will find a way to get money out of it. It's a real big dick move.