You may have heard about them in the news, through one of your favorite online shopping sites, or from a friend who always has the latest scoop on technology trends: cryptocurrencies, like Bitcoin, are a way to buy things online — or in person, using a mobile app — with sellers who agree to accept them.

Cryptocurrencies can be a fast and inexpensive way to pay for goods and services. They aren’t backed by a government or central bank, and they’re not insured, the way U.S. bank deposits are. They have value because users agree they have value.

The value of cryptocurrencies rises and falls — sometimes sharply — depending on demand. If the value goes down, there’s no guarantee that it will rise again.

Some payment systems offer legal protections if something goes wrong. For example, the law limits your responsibility for unauthorized use of your credit card to $50. There are no such protections for purchases made with bitcoins.

Bitcoin users store their bitcoin addresses in a “wallet” — either on a computer or other data storage device, or through an online wallet service. If you use Bitcoin, encrypt your wallets and back them up. If your Bitcoin wallet files are accidentally deleted, tampered with by a virus, or stolen, your funds could be gone. Or if the company behind your digital wallet fails, or is hacked, you could lose your funds. That’s already happened to some Bitcoin users.

Bitcoin users have private and public virtual keys. It’s important to secure your private keys, and not share them with anyone. They’re the only way you can use or transfer your bitcoins.

If you’re considering Bitcoin mining as way to make money, read up on the FTC’s recent case against Butterfly Labs. And if you’ve had a problem with a bitcoin-related product or service, file a complaint with the FTC.