Today I was just browsing eBay on my Macbook Pro and all the sudden a window takes over my screen saying that my computer needs a virus scan. Then another window pops up and asks me if I want to perform the scan. I click cancel but it does nothing, I can't get out of it. So I then click okay and it starts showing that it is scanning files. The window looks like something from Windows Vista. I am then able to get out of the window that was supposedly scanning for a virus. I close safari and then get back into Safari and everything seems fine. I am on my Macbook for another hour and everything is fine. Do I somehow have some kind of virus?