I was just looking at a news site when my iMac (mid 2009, running El Capitan) suddenly started behaving strangely. Everywhere I clicked a large gray Safari emblem appeared on the page, and I got a message saying my Mac is infected, and to call 888-342-4947. It also said that if I left the page the Mac would be permanently damaged. I figured it was a spoof, but the Mac was downloading files. It wouldn't shut it down, so I hit the on/off button and powered down. When I rebooted, the Mac was still downloading files, so I tried to force quit Safari, and got a message saying it has 11 more files to download. I had it force quit anyway. Now, how do I get rid of and files it already downloaded, and make sure they don't open? I'm worried Thanks.