The Internet has just served its billionth customer.

In December, the total global Internet audience surpassed one billion users, according to Internet traffic measurement firm comScore (NASDAQ: SCOR). In a new report, the research firm said that the Asia-Pacific region continues to claim the lion's share, accounting for 41 percent of Internet users worldwide -- about 416 million.

Europe came in second with about 283 million Internet users, accounting for 28 percent of the wired population. With 185 million users, North America came in third at 18.4 percent, comScore said. Latin America accounted for 7 percent of total users with 75 million, and the combined Middle East and Africa region together attained 5 percent share, or 49 million.

"Surpassing one billion global users is a significant landmark in the history of the Internet," Magid Abraham, comScore's CEO, said in a statement. "The second billion will be online before we know it, and the third billion will arrive even faster than that."

Even as the world's online population continues to grow, the findings also demonstrate the U.S.'s declining share of Internet usership. That's in spite of the fact that the U.S. government had a large role in setting up and directing much of the Internet's early growth -- and still maintains close ties to key Internet authorities today.

Concern over the U.S.'s place in the Internet economy also stemmed from findings that showed that the country is falling behind in affordable broadband. A report in 2007 claimed that U.S. had slipped to 15th place in per capita broadband adoption, down from fourth place in 2001. Such findings have since prompted legislators and policymakers to seek ways to encourage the spread of high-speed Internet to underserved Americans.

Most recently, that's involved discussion of including funds to encourage broadband rollout in the economic stimulus package now being debated in Congress.

On a country by country basis, China leads with the biggest audience on the planet: comScore counted 180 million users online in the country, representing 18 percent of the total worldwide audience.

The U.S., with its 16.2 percent share, is in second place with 163 million users. Japan rounds out the top three with 63 million, or 6 percent share of the Internet population.

The report counted only Internet users 15 years older who logged on from home or work PCs -- so it excluded the growing population of those using the Web via mobile phones.

Top sites on the Internet

comScore also ranked the most popular sites online. The top Internet site worldwide was search colossus Google, with 778 million visitors, and which reached 77 percent of all Web users.

Right behind was Microsoft's network of sites, which garnered 647 million visitors and reached 64.2 percent of Web surfers. Yahoo came in at No. 3, with 562 million visitors and 55.8 of the worldwide audience.

It was a photo finish between Time Warner's AOL properties and Wikipedia for the fourth- and fifth-place spots on comScore's list. AOL claimed the No. 4 slot with 273 million visitors in December, while Wikipedia received only 22,000 fewer visitors, comScore said.

Facebook dominated in the competitive social networking arena, according to comScore, which said the site grew 127 percent during the past year to claim 222 million visitors in December. That made it the top social site and seventh most-popular property worldwide.