If you're like most of us, you likely have a number of random user accounts that have been created over the years on a variety of different services. Sometimes it's an account on a website that you purchased something from once, or a service that you were indulging a passing interest in. Regardless of where it came from, the chances are that you have accumulated a significant number of these old accounts (also known as zombie accounts), and there is an even greater chance that they are still active.
It may not seem like it, but these accounts can actually pose a pretty serious threat to your personal information, and might even be an easy stepping stone from which your current and more important accounts are breached. It's no secret that most people reuse passwords across numerous accounts, and often have had the same passwords for years. When you combine reused passwords and old accounts across numerous platforms, and factor in that data incidents and breaches are becoming more frequent and often are more severe... the outlook isn't great for the end user. Cybercriminals can throw a lot of stuff at the wall, and the chances are that much of it will stick.
To protect yourself, you should probably try to create a list of old services that you've signed up for by looking for registration emails or confirmations, and closing the accounts if at all possible. To further protect yourself, you should NOT be using the same passwords for extended periods of time, and you should change passwords that you've reused on other platforms. If you want to learn more about the risks of zombie accounts, check out this article on Forbes.