But the fact SSN doesn't make sense is why people are questioning it. In fact I question if that's even a legal use for an SSN. How do you know they used your SSN for address verification?
SSN cannot directly be used to verify addresses, because there is no legal address information carried by SSN or the SSA. SSN is only legally used to verify
identity and SSN validity, and the verification services provided by the SSA is dedicated solely to this. The only way they could use SSN to verify address is to first use it indirectly as part of a background check, as in to first verify your identity, then carry out searches through state and public record databases to try and pinpoint your address through other databases. Which is both expensive and unreliable for this purpose where there are better ways to verify residency.
pokerstars does just fine verifying addresses the old fashioned way -- by requiring players to provide documentation proving their address. Then IP geolocation and anti-VPN/RDP technology can be used to track where players are accessing the service from.
From reading the WSOP.com location verification thread on 2+2, they're using IP geolocation or cellphone triangulation, via the Locaid service. SSN is never mentioned once. The problems people are reporting seem to be around either unsupported cellphone carriers, like TracPhone/Spring, or (as expected) the fact that IP geolocation is maybe 50% reliable. The WSOP.com reps are telling people to either change their cellphone carrier or their ISP. LOL.
Here's an article describing the Locaid service used by Ceasars Interactive for UB and WSOP address verification. It describes some of the methods used -- SSN is never mentioned (not surprising). It uses cellular and IP geolocation for broad region location, then when it needs to pinpoint you (such as the example of being by the casino pool, where in NV it's apparently illegal to bet from) it uses wifi search to see if you're in range of known hotspots.
