If shopping online gives you spasms of identity-theft fear, you might be interested in certain protections that some credit cards have started building into their services.

If you really want to sneak around online, find out whether your credit card company issues alternative account numbers specifically for Internet shopping. These numbers may be used one time, or for a limited time with a merchant, depending on the credit card. They allow you to purchase goods without putting your real account number into a Web purchase form.

Using your online alter ego
Various card issues have various names for these alternative account numbers. Citibank (NYSE:C), for example, calls them "virtual account numbers." They offer the benefit through some of their cards and allow users to generate a random number for use while shopping online.

Bank of America (NYSE:BAC) calls its program ShopSafe, and it allows users to create a unique, temporary card number for making online purchases. Similarly, Morgan Stanley's (NYSE:MS) Discover card allows credit card customers to use what it calls "secure online account numbers" for different merchants. If that secure number gets compromised, you can deactivate it without canceling your Discover account.

The virtual numbers allow you to buy whatever you want without using your real credit card number online. The merchant won't have your true account number in its files. It's a system that won't work, however, for many goods that you purchase online and then pick up in person. Buy something like movie tickets, for example, and you'll probably be asked to show your credit card for identification. When you show up at the ticket window, the number on your credit card won't match what you used online.

Passwords to buy
Another online security program, offered in similar forms by Visa and MasterCard (NYSE:MA), allows users to establish a private code or password for Internet shopping. Once you've registered and created the code, you'll be prompted to enter it when purchasing items online. Being forced to provide the code at checkout provides an extra measure of security, assuming you're the only one who knows the top-secret password.

To take advantage of this idea, you'll need to make sure your financial institution participates in the program. You'll also have to see whether your online store of choice participates. On the downside, it may not provide much protection against identity thieves who stray from participating merchants.

Automatic protection
It makes sense to reach for your credit card when shopping online. Credit cards hold you liable only for the first $50 in fraudulent charges if a credit card thief gets a hold of your number. Some have zero-liability programs that even waive that amount in cases of fraud.

This is one place where an ounce of prevention can prevent a major headache. Even if you're using all of the security tools your credit card offers, you'll want to supplement them with some basic cloak-and-dagger habits.

Guard your identity. Keep an eye on your receipts and your mail. Many stores and banks now only print the last four digits of your account number on paper, but you'll want to be vigilant anyway. Shred anything you're tossing that has identifying information, like credit card account numbers, and stop the thieves from simply plucking your identity out of your trash can.

Keep your secrets. Don't write any of your PINs or other security codes on your cards or keep them in your wallet. With a million passwords to remember, it can be tempting, but remember that you're just making a thief's day much easier. Try not to choose an obvious number, even if you think it will be easy to remember.

Read your statement. Keep an eye on your credit card statements, and you'll quickly notice whether a thief uses your card to purchase $10,000 in collectible baseball cards on eBay. If anything looks unfamiliar, suspicious, or just plain wrong, immediately raise a red flag.

When it comes to your credit, you can never be too careful. For more on using your credit wisely and avoiding identity theft and credit card fraud, check out the Fool's Credit Center.

Related Foolishness:

Bank of America is an Income Investor selection, eBay is a Stock Advisor recommendation, and MasterCard is an Inside Value pick.

Fool contributor Mary Dalrymple has watched too many spy movies, and she does not own stock in any company mentioned in this article. She welcomes your feedback. The Motley Fool has a disclosure policy.