There’s a new app to find out which of your so-called friends unfriended you on Facebook: Who Deleted Me. Available for both iPhone and Android devices (and as a browser extension for Google Chrome), the free app became quite popular this past week.

So how does it work? After downloading the app and opening it for the very first time, Who Deleted Me will save a copy of your list of Facebook friends, according to Business Insider. Then, the next time you visit the app, it will compare your current friends list with the saved version and let you know if someone deleted you, if you deleted a person or if a person just deactivated their account.

Other benefits of the app include a list of newly acquired Facebook friends and being able to see when the last time your friends logged in to the social media site, reported BuzzFeed.

A major disadvantage of the app is that you can only see who has unfriended you since you first started using the app, not “who unfriended you in 2012,” as pointed out by Business Insider.

Who Deleted Me became so hot earlier this week—BuzzFeed reported that 330,000 people signed up for the service this month alone—that some people had trouble using it. “We're experiencing much higher than normal traffic currently so Who Deleted Me is running slowly. We're working on a fix!” said the company via Facebook July 6. And, on July 7, it said: “We're upgrading to some bigger servers.”

The app originally launched in 2009 and worked directly with Facebook, according to Mashable. However, it was soon disabled by Facebook because it created a “negative user experience that is in violation of our Platform Policies,” according to Business Insider.

Who Deleted Me is not the first of its kind. Last year, the browser extension Unfriend Notify became available for Firefox and Chrome, said Business Insider. There’s also Unfollowers.com, which tells you who is no longer following you on Instagram and Twitter, and WhoUnfollowedMe?, which tracks those that unfollow you on Twitter.