The problem with SSNs is how short they are. 9 digits. Even if you hash them, it's not that hard to make a 10^10 - 1 rainbow table. It's the same problem with

The problem with SSNs is how short they are. 9 digits. Even if you hash them, it's not that hard to make a 10^10 - 1 rainbow table. It's the same problem with IPs (v4). You simply cannot store them at all if you care about your customers' privacy.