U.S. consumers spent US$25.5 billion online between Nov. 1 and Dec. 23, compared with $26.3 billion during the comparable period last year, which was Oct. 27 through Dec. 18, according to comScore. Dec. 23 was the last day to purchase with the possibility of delivery by Christmas Eve, the company said.

The results fell short of comScore's prediction before the season, which had called for flat sales. Although there were some hopeful moments for online retailers, such as a year-over-year sales increase of 15 percent for the Monday after the U.S. Thanksgiving holiday, the weak economy slowed consumers down, according to comScore. There also were five fewer shopping days between Thanksgiving and Christmas, the company noted.

The bad news went beyond just the holiday season. The fourth quarter as a whole will mark the first quarter since 2001 with lower online sales than a year earlier. Sales for Oct. 1 through Dec. 28 were about $36.8 billion, down 4 percent from $38.4 billion in the fourth quarter of 2007, the company said.

But shoppers visited online stores more often during the holidays, with total unique visitors to all stores, between Dec. 1 and Dec. 24, rising 5 percent to just under 180 million.

The top e-commerce site in visits remained eBay, with 85.4 million unique visitors, but it suffered a 4 percent drop from a year earlier, comScore said. The sites operated by Amazon came in second, with more than 76 million, an increase of about 7 percent. Wal-Mart trailed in third place, with 51.5 million, but it gained 4 percent from the previous year.