Well I guess 50,000 is small in comparsion to Cox's footprint. Especially since I am going to bet most of those were idle accounts.
While everyone is resetting passwords, it might be a good idea to reset your security question. Probably not needed, but better to error on the side of caution.
Kind of wish Cox allowed users access to the IP's used to sign into accounts. Would be handy in both troubleshooting, and security threats like these. Gmail has such a function and I use it alot to keep tabs on my accounts.