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Digital media research firm comScore Inc. (NASDAQ: SCOR) has released its ranking of the top 50 U.S. web properties for March and the list is topped, once again, by the usual suspects. comScore counted a total audience of unique website visitors of nearly 223 million, more than two-thirds of the total U.S. population, and about 1.5 million more than the total February count.

Leading the pack are sites owned by Google Inc. (NASDAQ: GOOG) with more than 192 million unique visitors. Yahoo! Inc. (NASDAQ: YHOO) sites attracted more than 191 million visitors to nab second place, followed by Microsoft Corp. (NASDAQ: MSFT) with about 166 million unique visitors, Facebook Inc. (NASDAQ: FB) with about 148 million, and Amazon.com Inc. (NASDAQ: AMZN) with about 121 million. Aol Inc. (NYSE: AOL) with more than 114 million and Glam Media with 104 million were the only other sites to top 100 million unique visitors.

Compared with February’s data, Yahoo’s sites gained about 5 million visitors, while Google sites saw a rise of more than 2 million. Facebook’s unique visitor count was up by about 4 million, and Microsoft had about 3 million more unique visitors in March. AOL’s count rose by about 4 million.

Wal-Mart Stores Inc. (NYSE: WMT), in 25th place, was the only traditional retailer to make the top 50 list.

comScore noted that traffic to pharmacy sites jumped in March as allergy and cold sufferers tried to find relief. Toy sites and teen-oriented sites also spiked, as did sports sites during the college basketball playoffs and the beginning of baseball season.

Among syndicated comScore Ad Focus entities, the ‘Share This’ platform led with an 95.4% reach to Americans online, with Outbrain at 86.7% reach, Yahoo at 85.9% reach, Google at 83.4% reach, and Facebook at 66.1% reach. “Reach” is the percentage of the total 223 million unique visitors in March that viewed an ad served by the particular platform.

comScore’s press announcement is available here.

Corrected from May 1, 2013, version.