Mary Lu Marr of Dublin, Calif., displays just a few of the items she has won playing hundreds of sweepstakes a day online at her home. She recently won a $50,000 grand prize.

WALNUT CREEK, Calif. — Each day around 8 a.m., retired grandmother and occasional actress Mary Lu Marr flips on the TV, pulls out her trusty laptop and gets to work at her “part-time job.”

For the next few hours, the Dublin, Calif., woman will enter hundreds of sweepstakes, filling out forms and transcribing product codes. This has been her hobby for more than 40 years, and persistence has paid off - she has won cruises, a car, home theaters, even a year’s supply of Godiva chocolates.

Her latest haul came in February with a $50,000 grand prize from lunch meat maker Carl Buddig.

“I really don’t know anyone else who does it like I do,” Marr said. “It’s obsessive.”

But she isn’t alone. Industry experts believe there may be hundreds of thousands of Americans just like her. They even have a word for the phenomenon — “sweepers.”

“The term ‘sweeper’ is someone who enters sweepstakes as a hobby,” said Carolyn Wilman, a Canadian author of two books on the subject. “It’s no different than sitting around with trains or coins or whatever people do for fun, except ours can take you on crazy adventures.”

Wilman, who calls herself “The Contest Queen,” attended her first sweepstakes convention in 2005. A daily sweeper, she occasionally wins big, like her trip to the 2010 Winter Olympics, or a costume party dinner on the Hogwarts set during a London filming of a “Harry Potter” adventure.

“You’re always waiting for the call or e-mail,” Wilman said. “I’m probably the only person who looks forward to Mondays because that’s when the mail service starts back up.”

An estimated 55 million Americans enter sweepstakes each year, according to one industry guide. The contests serve a purpose: companies collect personal data on those who enter and generate brand interest. Sweepers, who tend to sign up regardless of the brand, undermine those goals, but not everyone thinks they’re a bad thing.

“The perception is that no one wants them entering and stealing the prizes from customers,” said Jeff Renda of Sweepstakes Pros, a San Jose, Calif., company that runs sweepstakes nationwide. “But these people are consumers, too. Even if they aren’t specific to the brand, it doesn’t matter in the long run; you just have to make sure you’re hitting the market goals you want.”

Thanks to the Internet, what once took extreme sweepers much time and postage is now as easy as a few clicks of the mouse.

Sweepers turn to online or print newsletters. Craig McDaniel, a.k.a “Mr. Sweepy,” is president and founder of Sweepstakes Today. His free online newsletter boasts 300,000 members, of whom about 3 percent enter 50 to 100 giveaways each day, he said. Their average age is 45, and three-quarters are female.