Yes, social security does indeed have investigators to investigate certain claimants that they believe are no longer disabled. Every year tons of money is being paid out, to the non-disabled that are claiming disabled, when in fact it could actually be going to the truly disabled.

Not sure if the man in the van is an investigator or not. Sounds he could be. Either that or a stalker. Call the cops and get him investigated. He shouldn't be there without legal business. If you're truly disabled then you have no worries with the investigation.