Google had more than 1 billion unique visitors during the month of May, according to ComScore. It's the first time any Internet company has had that many unique visitors in a single month. Microsoft came in second place with 905 million unique visitors in May, while Facebook had about 714 million. Advertisers are increasingly concerned with the amount of time spent on websites, as they try to gear graphical and interactive ads toward users. In terms of time users spend on a site, Facebook surpassed Google and Microsoft last year, and in May users spent 250 million minutes on Facebook, as opposed to only 200 million minutes on Google.