Cyber Monday: How to Keep Your Credit Card Information Safe

— -- It's the most wonderful time of the year -- until your credit card information is compromised.

An estimated 140 million American shoppers started their holiday shopping in stores and online over Thanksgiving weekend, according to the National Retail Federation.

While many of us are dreaming of deals on Cyber Monday, it's important to remember that criminals are on the prowl, targeting unsuspecting shoppers and trying to steal their passwords and credit card information.

"If you're shopping at a site you haven't been to before, you kind of do so at your own peril," Tim Ryan, a former FBI investigator and managing director of the cyber investigations practice at Kroll, told ABC News.

While it doesn't necessarily mean avoiding those sites, it's important to make sure they're secure before entering any personal information.

Many browsers show this by displaying a padlock icon near the address bar or the upper right corner of a window. Another easy way to make sure you're on a secure site is to make sure the URL starts with "https://".

Ryan said he advises shoppers to "be hesitant" of reacting to any emails or phone messages they may receive from people claiming to be from a store or their bank.

"People are going to be sensitive to the timely nature of their purchases and criminals know this," he said.

One such example he's seen is a scam email claiming a user's credit card may be deactivated soon unless they click a link that essentially leads them into a criminal's trap.

"If your bank allows you to get email or text alerts about whenever your card is used, I think that's really an excellent way to monitor what is happening with your card," Ryan said.

One of Ryan's other tips for staying safe may surprise shoppers: It's OK to let a trusted website, such an Amazon, store your credit card information.

"Entering your card once is more secure than you continually having to enter your credit card time and time again," he said.