The last time I set up a new computer, I was surprised to find that installing a password manager has become a critical part of getting the system ready to use.

It used to be that you could pick a few unique passwords for critical services like your primary email and banking sites, and reuse some passwords for less important sites, and maybe remember them all. But when so much of what we do happens online in so many places with so many different levels of security (and visibility), the attack surface is huge. Add in how many criminals and others are trying to break into those sites, and it’s no longer safe to reuse passwords.

Why?

If one site gets hacked, and you use the same password at another site, someone will try it just to see if it works.

The only way to protect against that is to use a different password on every site. And unless your online activity is very narrow, chances are you can only memorize a few of them. You can stretch it out with mnemonics like XKCD’s passphrase scheme, but eventually you’re going to have to record them somewhere. Putting it in a text file or spreadsheet is bad, because anything that gets onto your system can read it, but password managers are designed to encrypt them.

You still have to protect the master password on that file, but now you don’t need to worry that when someone finds your old MySpace password, they’ll start buying stuff on one of your shopping accounts, or hijack your Twitter as part of a harassment campaign, or use your email account to send malware to all your friends.

LastPass is a popular one. It’s cloud-based, which makes it convenient to use on multiple devices, but you do have to trust them. If you’d rather not trust your passwords to someone else’s computer, you can go with an offline manager like KeePass, which stores everything locally on your system in an encrypted file.