That is why we want you to reset your password.
First, it will be required of course that the passwords are changed so as not to result in anyone else getting access through any possible leaks or cracks; secondarily but just as importantly for many people signing up with reused credentials has caused trouble: forgotten codes which can make accessing bank accounts difficult if they're compromised online - this could mean going without internet service until remedy becomes available (or being forced out by creditors). As well "forgotten" email addresses/ User-ID's etc may prevent certain services such.