If you chose to avoid the stampedes at brick and mortar stores on Friday—as I did, after awakening from a kingly coma and brushing a pile of pie crumbs off my belly—and plan instead to shop online, then please read on. I’ve got a simple, yet substantial cybersecurity tip for you.

First, context: Cyber Monday, the e-commerce bonanza that kicks off the beginning of the week, is set to be the biggest payday on record for electronic merchants. (We at Fortune prefer Cyber Saturday™, of course.) Crooks are no doubt eyeing the opportunity to score. Don’t let them.

One easy way to prevent hackers from profiting off the occasion involves securing your digital identity. So, the advice: Add what’s called multi-factor authentication to your online shopping accounts.

Here’s how it works. Whenever you log in to an online profile, the website’s entry field will prompt you to submit a second passcode, one on top of your usual password. This will either be a string of numbers that is sent directly to your mobile phone via text message, or a string of numbers that can be read off an “authenticator” app, which generates one-time passcodes. (See Google Authenticator (GOOG), for example.)

Multi-factor authentication—sometimes called “two step” or “two factor” authentication, or abbreviated “2FA”—is one of the simplest measures you can take to lock down your digital persona. Think of it as adding another lock to your money vault. Amazon (AMZN) recently added the feature to its website. Go, take advantage.

As you know from this holiday season, there are many things in life to be thankful for. Cybercrime is not one of those things. Take a stand against it; here’s a list of the places that let you armor up.

A version of this post titled “Step one, step two” originally appeared in Data Sheet, Fortune’s daily tech-business newsletter. Subscribe here.

Follow Robert Hackett on Twitter at @rhhackett, or keep up with his cybersecurity, technology, and business coverage here.

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