State of the Art: Why You Shouldn’t Use Facebook to Log In to Other Sites

I’m going to quit using Facebook to log in to apps and sites online. You should, too.

That’s the most reasonable way to respond to Facebook’s announcement last week that a security breach allowed hackers to infiltrate the accounts of at least 50 million users, and possibly tens of millions more. The hack gave attackers access to not just your Facebook account but also possibly the many accounts you used Facebook to log in with — services like Instagram, Spotify, Airbnb, Tinder, Pinterest, Expedia, The New York Times and more than 100,000 other places online.

I say “possibly” because neither Facebook nor third-party sites seem to know the precise extent of the damage. In a statement on Tuesday, Guy Rosen, Facebook’s vice president of product management, said the company had “no evidence” that attackers breached other sites through the hack, but that the company was building more sophisticated ways for sites to do their own deeper investigation.

But the mere possibility is highly troubling — and if the hack allowed access to any other sites, Facebook should be disqualified from acting as your sign-on service.

This is a classic you-had-one-job situation. Like a trusty superintendent in a Brooklyn walk-up, Facebook offered to carry keys for every lock online. The arrangement was convenient — the super was always right there, at the push of a button. It was also more secure than creating and remembering dozens of passwords for different sites. Facebook had a financial and reputational incentive to hire the best security people to protect your keys; tons of small sites online don’t — and if they got hacked and if you reused your passwords elsewhere, you were hosed.

But the extensive hack vaporizes those arguments. If the entity with which you trusted your keys loses your keys, you take your keys elsewhere. And there are many more-secure and just-as-convenient ways to sign on to things online.

The best way is to use a dedicated password manager — a service, like LastPass or 1Password, that creates and remembers strong passwords for different sites. Operating systems and browsers are also getting better at managing passwords; newer iPhones, for instance, let you unlock sites with facial recognition, which is just as convenient as pressing Facebook’s button.

If for some reason you don’t want to use a password manager, you can use another tech giant’s sign-on service. When presented with different ways to sign on to sites, you can choose Google or Microsoft instead of Facebook.

Yes, it’s possible those companies could be hacked one day, too. After all, Yahoo was hacked, as was LinkedIn, as was Equifax. But at this moment, a sign-on service by Google or Microsoft has one big advantage over Facebook’s: Those companies did not lose control of 50 million people’s accounts, and Facebook did.

I decided to quit using the social network as a login service after chatting with Jason Polakis, an assistant professor of computer science at the University of Illinois at Chicago, who has studied the security of sign-on services like Facebook’s.

Mr. Polakis allowed that there are tremendous convenience benefits and even some security benefits to a single sign-on. “Obviously, big companies like Facebook and Google have amazing engineers, and their security practices are generally ahead of the curve compared to other, smaller websites,” he said.

But no company, not even one as big and wealthy as Facebook or Google, can guarantee perfect security.

And in some ways, Mr. Polakis said, Facebook’s size and complexity work against its security. The Facebook hack, for instance, seems to have been caused by three different bugs acting in concert.

“The codebase of these services is massive,” Mr. Polakis said. “You have different teams working on different components, and they can interplay in different ways, and you can have a crazy hack that no one expects.”

The other danger to signing on to everything with Facebook is the threat of phishing. Even if millions of Facebook accounts hadn’t been hacked, people’s individual accounts are hacked all the time through online trickery. Single sign-on compounds the damage — whoever hacks your Facebook account gets access to everything else you tied to Facebook.

Why is a password manager a better way to protect yourself than signing on through a big platform? Password managers can also be hacked, Mr. Polakis said, but “compared to massive platforms that have millions of different lines of codes and different functionalities, a password manager has one specific job, and so it minimizes the chances of something going wrong.”

I asked Facebook for a counterargument to stop using it for signing on. A spokesman said Facebook’s sign-on was still more secure than the weak passwords that people create and reuse for everything.

That’s not a bad point. Password managers aren’t as convenient to use as Facebook’s button; if people respond to the Facebook hack by rolling their own passwords instead of using Facebook, that may be worse for everyone.

The spokesman also noted that Facebook was taking this hack very seriously and had been investing heavily in security and privacy practices during its last two years of scandal.

I don’t argue otherwise. I believe Facebook is taking this seriously. At some point, maybe, Facebook will regain my trust enough to handle my digital keys.

But it will do so only if there’s some cost to losing them. For now, that cost is: When I see the blue Facebook button offering an easy way to sign up for this or that digital doodad, I’m not tapping it.