Security researcher Arne Swinnen was unlocking some old Instagram test accounts recently when he noticed a problem. The account verification page for reactivating lapsed accounts gave him the ability to take full control of other lapsed accounts as well.
Overall, Swinnen estimates he could have taken over 1 million Instagram accounts, getting access to their photos, followers and even location information. Facebook, which owns Instagram, quickly fixed the problems, but this situation is a good reminder for everyone about the dangers of old accounts.
Old accounts on the Internet don't die. They can stick around for years or even decades with whatever information you put in them originally. A data breach, site security flaws, or just the fact you used a poor password, can give a hacker access to steal that information or use the account for other purposes, such as spamming or tricking your friends.
Even if the hacker gets nothing more than your email address, that's enough to target you for a phishing scam. And if you're in the habit of reusing your password, or creating passwords that are very similar, a hacker could potentially break into the accounts you do care about.
That's why every once in a while, you need to take the time to permanently shut down accounts you don't use anymore. Even if you don't remember every account you'd created, a simple browser trick can help you find them. If you aren't sure how to permanently delete a particular account, this site can help.