Recently Epsilon got hacked causing a ton of fake emails to be sent out to people all over the place. The problem is that people are giving away personal information because they have been fooled into doing so by emails that say something like "Your account has been compromised please enter your password to verify your account." This is a technique called phishing and can cause all sorts of problems for anyone who falls victim.
The most immediate threat is the possibility for people's identities to be stolen on a massive scale and have them all end up accumulating a lot of false charges. This means that there would have to be an investigation into each account that was tampered with and the person whose account it is would have no access to it for roughly a week. This would hurt the economy because people would all of a sudden have to be extremely careful with their money, especially if they have all of their money in one account. The other problem is going to be for any company that deals with online security because people will start to have their doubts about even the most secure companies after such a large breach. This corporations could end up using smaller security companies less, causing them to go bankrupt. This wouldn't be any good because it would mean that there was less competition. With less competition in the online security section of the market then prices could rise. This could end up causing a rise in prices on everything that the company sells because they would have to pay for a more expensive security system and that would be bad for the consumer. Overall this is just a bad situation that will probably have a large amount of consequences.