So I know my 27 inch 2017 iMac is not infected but every so often when I go on my Audio video forum the screen gets taken over by a sign saying my iMac has three viruses and sometimes a voice will come on saying same thing. I shut down safari and it's gone.Checked my download folder and nothing suspicious there. Before this started I would get an announcement my flash player outdated which is not true and I just ignored that.Now that's gone but this virus announcement has taken its place Any way to get rid of this or just ignore it?