Cyber Monday wasn’t just about sales.

On one of the busiest online shopping days of the year, the Justice Department announced that it shut down 150 Web sites selling counterfeit goods ranging from sports jerseys to handbags to the popular P90X exercise program. The operation was part of a campaign launched last year that has targeted more than 350 sites visited by millions of consumers.

“For most, the holidays represent a season of good will and giving, but for these criminals, it’s the season to lure in unsuspecting holiday shoppers,” said John Morton, director of Immigration and Customs Enforcement, which spearheaded the operation.

According to the National Retail Federation, a trade group, nearly 123 million people planned to shop Monday, up nearly 15 percent from last year. Conceived as a way to keep the holiday spirit — and spending — going once workers returned to their cubicles after Thanksgiving, Cyber Monday now rivals Black Friday in popularity and sales.

But the rise of online shopping also comes with potential perils for consumers, who may unwittingly buy fraudulent merchandise or become victims of identity theft. According to the Federal Trade Commission, complaints about identity theft have tripled over the past decade to more than 250,000 last year. Meanwhile, fraud accounted for about half of the agency’s 1.3 million complaints.

The Obama administration is slated to launch a public awareness campaign on Tuesday on intellectual property theft. In addition to scamming consumers, officials said, buying fake merchandise diverts much-needed sales from legitimate businesses. According to government data, federal agencies seized $188 million worth of counterfeit products last year.

“We are aggressively targeting those who are selling counterfeit goods for their own personal gain while costing our economy much-needed revenue and jobs,” Attorney General Eric H. Holder Jr. said. “Intellectual property crimes harm businesses and consumers alike, threatening economic opportunity and financial stability.”

Many of the domain names seized in the Cyber Monday crackdown may have seemed legitimate to consumers:, and, for example. A Justice spokeswoman said the sites now display a banner notifying consumers that the domain name has been shut down. Several sites also include an ICE video highlighting the economic consequences of intellectual property theft.

To avoid scams, consumers should be on the lookout for inaccurate grammar and frequent misspellings on sites and make sure that contact information is available, Justice officials said.

Meanwhile, the Consumer Federation of America advised shoppers to be wary of online contests, as they may carry viruses that can compromise a computer’s security. The group also encouraged consumers to view their credit reports for accuracy or signs of fraud.

“Consumers share a lot of personal information during the holidays as they shop for gifts, online and offline,” said Susan Grant, CFA’s director of consumer protection. “Many people also chat about their holiday plans on social-networking sites. It’s important to remember to guard your privacy, during what can be a frantic time for many people.”