Sayid is attacked at St. Sebastian's

After Jack left with Dr. Ariza, a man posing as a nurse (whose name is listed as Tony in the casting call) comes into Sayid's room to administer medication. He pulls out a dart gun and fires two darts at Sayid's bed but he has disappeared. Sayid attacks Tony from his side and subdues him by choking him with an IV line. When Sayid asks who he's working for, Tony says there is an address in his pocket. Sayid then shoots him with two darts and pulls his wallet from his pocket. The address in the wallet is "42 Panorama Crest" which when Ben and Jack come into the room, Jack points out that it is Kate's address.

The big question here is still, who are these operatives that have been following Hurley and attacking Sayid working for? Also, why did Tony have Kate's address?