American federal authorities just issued a new consumer warning for shoppers. Hidden skimming devices, once thought to be commonly attached to gas station pumps and ATMs, have recently gone high-tech. Herb Stapleton, section chief for the Federal Bureau of Investigation's cyber division told CNBC on Friday: "It's hard to put really - definite numbers around it. But one thing we know for sure is that millions of credit card numbers have been stolen, even over the course of the past two years."

The new type of skimming is called e-skimming or magecart. Through the process, cybercriminals can gain access to people's personal and credit card information in a variety of ways. Criminals can compromise a web server directly or breach into a common server that supports many online shopping websites to compromise them all.

Stapleton asserted it is nearly impossible for consumers to determine whether their personal data has been skimmed before the actual e-skimming occurs. Randy Pargman, senior director for threat hunting and counterintelligence at Binary Defense, an Ohio-based cybersecurity firm that monitors companies' computers, said many of the affected victims of e-skimming are in the retail space.

CNBC reported some victims of skimming are Macy's (M  ), Puma's (FWB: PUM) Australian website, Ticketmaster's (LYV  ) British website, and British Airways (LSE: IAG), though the firms named have not responded to the report yet. Pargman added any online retailer is likely concerned with e-skimming.

But e-skimming is not the only type of sophisticated online scam on the rise. Fraudulent robocalls from Indian call centers can also be dangerous. The callers might try to impersonate federal agencies or multinational corporations in an effort to persuade people to fork over personal info. Also, as tax return season starts, more scammers will be calling people about fake tax debts they owe and try to fraudulently claim large tax refunds first. The elderly and new immigrants are especially vulnerable to these two scams, due to a higher probability of ignorance of how the scams work.

The good news is people can easily protect themselves from e-skimming and other scams by shopping with credit cards instead of debit cards, using a virtual credit card number for online shopping, and monitoring their accounts for suspicious activity and reporting swiftly to their banks and credit card companies. Credit cards offer better protection against unauthorized charges than debit cards and often feature dispute periods of 3 months to up to 6 months. Virtual card numbers can prevent attackers from stealing real credit card info.

For robocalls and tax scams, people might find it prudent to avoid answering phone calls from unknown and out-of-state numbers, as well as never believing anyone who calls claiming to be a tax or federal agent. As cyberattacks and scams become more prevalent in the digital age, consumers should stay vigilant to protect their data.