The purpose of e-on saying they have been hacked since 2013 is to warn customers. If you have used credit/debit cards with the site in that time frame it is a good idea to go to your bank and request new cards issued, also if you use a shared password it is good idea to go onto the other sites with the same password and change it. The "hackers" are like parasites, the idea is not to destroy the host but to make the most profit from it.