Almost all of us have signed up for a free trial we then forgot to cancel before getting charged for the next month or have felt uneasy entering credit card information on a sketchy website. I discovered virtual credit card numbers several months ago and now use them for both these cases.

Virtual credit card numbers (VCN) are credit card numbers that aren’t associated with a physical card. They are usually tied to your regular credit card account, and charges to the VCN will show up on that credit card statement.

VCNs have two great features on top of regular credit card numbers. You can set the expiration and maximum limit can be charged, and you can cancel them at any time. Let’s say I want to try Spotify Premium. It’s free for a month and $10 per month afterwards. I generate a VCN, set the limit to $1 with an expiration of one month, enter that number into Spotify’s website, and forget about it. Use a VCN when you’re wary that an online merchant might steal or is unable to protect your card info as well.

So how does one get a VCN? The only free and bank-sponsored credit cards I know of that offer them are Bank of America’s ShopSafe feature and Citibank’s Virtual Account numbers. (Amex seems to have discontinued theirs.)

There are cases when using a VCN might create more hassle than it’s worth. The two I can think of are booking a hotel room and needing to show your card when you arrive in person and returning a purchase and trying to get a refund.