You probably know that it’s not a good idea to use “password” as a password, or your pet’s name, or your birthday. But the worst thing you can do with your passwords — and something that more than 50 percent of people are doing, according to a recent Virginia Tech study — is to reuse the same ones across multiple sites. If even one of those accounts is compromised in a data breach, it doesn’t matter how strong your password is — hackers can easily use it to get into your other accounts.

But even though I should know better, up until a few months ago I was still reusing the same dozen or so passwords across all of my everything (though at least I had turned on two-factor authentication where I could). It’s just too difficult to come up with (and remember) unique, strong passwords for dozens of sites. That’s why, after much cajoling from co-workers, I started using a password manager — and it’s why you should be using one, too. Aside from using two-factor authentication and keeping your operating system and Web browser up-to-date, it’s the most important thing you can do to protect yourself online.

Why you need a password manager

A password manager is a secure, automated, all-digital replacement for the little notepad that you might have all of your passwords scribbled down in now, but it’s also more than that. Password managers generate strong new passwords when you create accounts or change a password, and they store all of your passwords — and, in many cases, your credit card numbers, addresses, bank accounts, and other information — in one place, protecting them with a single strong master password. If you remember your master password, your password manager will remember everything else, filling in your username and password for you whenever you log in to a site or app on your phone or computer.

You can generate, save, and auto-fill passwords with Google’s Smart Lock (in Chrome and Android) or Apple’s Keychain (in Safari and iOS), but a good password manager goes a lot further — it can proactively alert you when you’re reusing a password or when your passwords are weak and easy to guess or hack, and some password managers will even let you know when online accounts are hacked and your passwords have been exposed. For accounts that you need to share with family members, friends, or co-workers — a joint bank account or mortgage site, a shared Twitter account, or your insurance and medical records, for instance — many password managers offer family plans that make it simple to share strong, complex passwords without requiring multiple people to remember them or write them down.