More than 85% of Internet transactions are completed with a credit or debit card, according to Javelin Strategy and Research data cited in a January 2008 Wall Street Journal article.

Checks do not account for all of the other 15%, however. Most of it comes from alternative-payment methods such as PayPal, eBillMe and Bill Me Later.

Bill Me Later is the most widely accepted at top Internet shopping sites, according to Brulant. There are tradeoffs for using alternatives to credit cards, according to the Consumer Federation of America.

The alternative-payment methods do not use credit card numbers, which increases security. "But that means you won't have the same protections as if you were paying with a credit card," said Susan Grant, director of consumer protection for the group.

"[Fraud] coverage is extremely limited, and whatever protections the service does give you are voluntary," Grant said.

Still, there are ways to improve purchase protection, according to PayPal spokeswoman Amanda Pires.

"More than 50% of the service's transactions are completed with a credit card, which means those still are eligible for traditional credit card protections," Pires said.