Safari won't work, supposed "security issue"

I'm on an iMac using Yosemite 10.10.2 Recently when using Safari, another tab opened by itself with an "error window" saying http://safarisystemissue.com, an error has been detected and give an 800 phone number to call. I called the number and it doesn't go to the regular menu choices but a live person comes on asking how to help. That never usually happens. I hung up. Right now, I can't use Safari. It's completely locked up yet it's fine on my MacBook Pro. Can someone help?