In terms of page views, however, Yahoo led all global properties, followed by Google and Microsoft sites, ComScore Networks said.
A total of 713 million people age 15 or older used the Web in June, with 21 percent coming from the United States, followed by 11 percent from China and 7 percent from Japan. Microsoft sites had the highest number of unique visitors with 500 million. Yahoo sites were second with 481 million and Google sites third with 454 million.
In terms of page views, Yahoo sites led with 116 billion, followed by Google, 84 billion; and Microsoft, 75 billion.
"The big three properties continue to aggregate the largest worldwide audiences, dominating the rankings," Bob Ivins, managing director for ComScore Europe, said in a statement. "MSN, Yahoo and Google ranked as the top three respectively, each drawing more than 450 million visitors in June, approximately 200 million more than the next closest property."
While the big three continued to rule, a couple of upstarts found their way into the top 15. Online encyclopedia Wikipedia was ranked eighth with 128 million visitors, and social network MySpace.com was ranked 15 with 66 million visitors.