I clicked a link in a gmail message, and arrived at a page that looks like a news site. I clicked a similar link in the next gmail message, and arrived at a page that warns that this is an "attack page": https://docs.google.com/open?id=0B-mMfXyy8lylSkZTY2hNZG8zNUk
Now, I am sure that the first link I clicked was sent to me from the same email address, so I already entered an 'attack page'. How can I check if my computer has been attacked?