Some evil hackers are attacking the company’s servers housing the users’ accounts and the task is keeping them from gaining access to the data and downloading it.
One thing to lose (besides accounts getting compromised) would be reputation, the more data is pilfered the lower the reputation. You might get new users depending on the reputation and the amount of users reflects on the resources you can mobilize to keep the attackers at bay…
(But that would be an advanced feature, not something for the basic first iteration…)