According to a Microsoft study, a Windows computer out of four DOES NOT have any antivirus, making the chances to get infected within a month very high (I would say that it's almost guaranteed).
And you? Do you use an antivirus, or you like the thrill to reinstall Windows every week?
Moreover, they made a test: can you recognize a "fake" antivirus that will scare you of a fake virus just to steal you money for a fake cleaning?
Can you pass it?