Old accounts like this are a long term security risk for a few reasons. If you’re like millions of others, there has been a time when you were using the same (or substantially similar) passwords for lots of services, so a data breach at a service like that gives hackers database with thousands of people’s username and password pairs that will work at other sites. The bigger issue as that these accounts often have information that can be used to confirm your identity somewhere.
Those “recover your password” security questions, like first car or mother’s maiden name or name of first elementary school teacher. I had one friend once dismiss a big data breach someone by saying, “I don’t give true answers to those question. I have a set of fake answers that I use everywhere instead.” It took me explaining to him a few minutes before he realized that having the same answers to those questions everywhere meant that learning the fake answers from one site gave other people access to his accounts elsewhere. It doesn’t matter if the answers to the personal security questions are true, just whether they match the answers you’ve give before.
In theory, deleting old accounts should remove all of that kinds of information at the service in question. So, this article may be useful to more than a few of you:
I've loved reading for as long as I can remember. I write fantasy, science fiction, mystery, and nonfiction. For more than 18 years I edited and published an anthropomorphic sci-fi/space opera literary fanzine. I attend and work on the staff for several anthropormorphics, anime, and science fiction conventions. I live near Seattle with my wonderful husband, still completely amazed that he puts up with me at all.