A new study by ComScore claims that the majority of traffic to the top U.S. websites isn't domestic. It's international.

The study also found that the top ad-supported properties, including Google, Microsoft sites, Yahoo and CNET Networks, derive at least 70 percent of their traffic from non-U.S. users, ClickZ reports. These figures could come as a shock to marketers buying non-geographically targeted search ads on these sites.

"If you're not geographically targeting, there's probably some waste," said ComScore Europe EVP Managing Director Bob Ivins.

The international traffic percentages for some of the biggest domestic sites include Google at 79.8 percent of unique visitor traffic and 89.1 of pageviews from non-U.S. users, Yahoo sites at 75.9 percent of uniques and 67.2 percent of pageviews, and Microsoft sites with 79 percent of uniques and 75.4 of pageviews. Ask Network derives 57.4 percent of uniques and 39.6 percent of pageviews from abroad.

Ivins added that the online population is tilting away from the United States and traffic to U.S. sites from abroad should continue to grow - as should traffic to non-U.S. sites.