So Ms. Gonzalez waited until Monday, when she spent "most of the eight-hour workday" searching for an MP3 player and "dropping hints" to family members by forwarding links to her favorite products.

The most popular sites were eBay, with 11.7 million visitors Monday; Amazon, with 5.6 million; and Wal-Mart, with 3 million.

The name Cyber Monday grew out of the observation that millions of otherwise productive working Americans, fresh off a Thanksgiving weekend of window shopping, were returning to high-speed Internet connections at work on Monday and buying what they liked.

This year, retailers said they saw a significant spike in the number of visits that translated into sales. That shift, they said, indicated that consumers had researched products and prices at stores before heading into the office to make their purchase online.

"People knew what they wanted," said Georgianne K. Brown, executive vice president for marketing at Baby Universe.com That site, which sells gear for babies like toys, strollers and car seats, had a sales increase of 50 percent over the same day last year, even as the amount of time customers spent on the site fell by an average of one minute, she said.

Raul Vazquez, vice president for marketing at Walmart.com, said that "customers were more decisive in their purchases." Three million shoppers visited walmart.com on Monday, a strong showing, but not enough to overtake the Friday after Thanksgiving, when five million clicked onto the site.

To encourage buying, online retailers dangled the same kind of incentives used in their stores. BabyCenter offered a 10 percent discount on select items; CompUSA, free shipping; and Godiva, a gift with purchase. Dozens of stores also sent e-mail messages to customers dangling special deals Monday morning.