Shoppers were not the only ones busy on Cyber Monday.

So were federal investigators in Buffalo, who marked the day by shutting down 15 websites allegedly selling counterfeit New Era caps and other sports merchandise.

For the third year in a row, agents from Immigration and Customs Enforcement conducted a global operation targeting websites that prey on unsuspecting consumers.

In Buffalo, they focused on websites selling knockoff sports products, including New Era Cap Co. merchandise.

“These are not victimless crimes,” said U.S. Attorney William J. Hochul Jr. “When you buy counterfeit merchandise, you’re not only hurting the company, you’re hurting the company’s employees.”

As part of their investigation, federal agents made undercover purchases from websites suspected of offering counterfeit products and, once the goods arrived, attempted to confirm their authenticity.

If the goods were found to be counterfeit, the government then obtained court-approved seizure orders that allowed them to shut down the websites and obtain their domain names.

In a related case, agents also arrested Gary C. Hammer, 47, of Cheektowaga, and charged him with selling fake Microsoft software on Craigslist.

“It’s not only illegal, it’s a danger to the consumer purchasing it,” said James C. Spero, special agent in charge of the Buffalo office of Immigration and Customs Enforcement, Homeland Security Investigations.

Spero said counterfeit software can pose a risk to buyers, who may use it to store important personal or financial information.

“As far as we know, this is the first time he’s been involved in this type of activity,” Assistant U.S. Attorney Michael DiGiacomo said of Hammer.

The investigation into the 15 websites is continuing. One of the focuses will be the individuals who sold the knockoff caps and merchandise. So far, no arrests have been made.

Spero said the fake caps were made in China, but investigators are uncertain whether the sales involved distributors or middlemen in the United States.

The government’s nationwide crackdown targeted online retailers offering a wide range of counterfeit goods and resulted in the seizure of 132 websites.

The seizure of counterfeit websites has become an annual Cyber Monday ritual of sorts. It also came two months after Sen. Charles E. Schumer, D-N.Y., called for stronger action against manufacturers of counterfeit products, many of them in China, and the websites that market them.

Schumer said that New Era has lost $300 million in sales because of counterfeit caps and suggested the illegal activity has put the Buffalo-based company at risk.

Monday, Schumer announced that the U.S. Trade Representative’s Office has communicated New Era’s concerns about knockoff caps to high-level Chinese government officials. In addition, a Chinese website that provided a vehicle for counterfeiters to sell their products has removed 380 listings for New Era products, he said.

Federal authorities also offered consumers tips on how to avoid buying counterfeit products. They noted that many counterfeit sites sell their items at prices that are too good to be true and often use improper grammar or incorrect spellings on their web pages.

They pointed to one of the New Era knockoff sites that listed itself as “New Ear.”

“Spelling and grammar [are tip-offs],” said Nicholas Peruzzini, a special agent for Immigration and Customs Enforcement. “The grammar is incorrect in a lot of these.”