Wall Street Journal:
Yahoo Inc.’s revelation of a massive 2014 security breach might have reminded you of an old account or two you haven’t logged into for years.
No good comes from leaving details of your identity—alternate email addresses, date of birth and, yes, passwords—floating around the backwaters of the internet. Hackers who find their way into one account, dormant or still in use, can exploit details such as PINs or security-question answers to get into other accounts. That’s right, your old AOL Instant Messenger account could compromise your Facebook account.
It’s best to reduce your overall exposure. Think of it as a pruning exercise.
Before you start shuttering accounts, consider a few things. You might lose access to services you never knew were related. Your Yahoo account, for example, gets you into the popular photo site Flickr. Your Hotmail email address could be your login for Xbox Live, Office 365 or Skype.
Respect the finality of your decision—when you’re out, you’re out. But canceling isn’t always easy.