I have a MacBook Pro- 2011. I recently started having problems when using sites like eBay and other shopping sites. I have been looking for art pieces on-line and when I click on one, the page advances to the product description. When I then click the back arrow to return to the list of items and pick a new item to view, the page will advance, the new item will briefly appear and then it will revert to the prior item. This is sporadic, but driving me crazy. I can sometimes solve the problem by closing the website and trying again, but not often. It is enough of a problem that I am joining this website to find a solution! Could I possibly have a virus? How would I check?