Online spending reached $25.5 billion between November 1 and December 23, the company said, noting this was below its expectations for flat sales on the same period a year ago.

Apple Inc and Amazon.com were among the top traffic gainers in an overall bleak period, comScore said.

Apple sites attracted 35 million visitors between December 1 and December 24, up 19 percent from a year ago, while Amazon sites drew 76.2 million visitors over the same period, 7 percent more than a year ago. Wal-Mart also saw its website traffic rise by 4 percent to a total of 51.5 million visitors.

Online auction site eBay Inc was the most visited retail site with 85.4 million visitors but its traffic declined 4 percent.

Electronics retailer Circuit City, which filed for bankruptcy, saw traffic fall off by 21 percent to 15.5 visitors.

A combination of five fewer shopping days between Thanksgiving and Christmas and the recession made the season particularly tough for retailers, Gian Fulgoni, comScore chairman, said in a statement Tuesday.

(Reporting by Elinor Comlay; Editing by Gary Hill)