The SECUR-T's are the police force of the BNL starliner Axiom. They try to keep things in order aboard the ship. After WALL-E accidentally freed the reject robots from the Repair Ward, they are constantly chasing the malfunctioning "rogue robots". They start to consider WALL-E and EVE as rogues as well.
Later, AUTO summons all available SECUR-T's to stop EVE and WALL-E, who are trying to place the plant in the Axiom's holo-detector. Those SECUR-T are then destroyed mainly by a malfunctioning HAN-S.
However, not all SECUR-T's were destroyed. When EVE broke out from the garbage disposal with M-O and WALL-E, they encountered a single SECUR-T unit who was then scared by EVE and went into hiding in a closet after taking a new picture of them.
It is possible that he was the SECUR-T unit seen on Earth during the credits. He was helping the humans and the other robots by constructing a large building by grabbing bricks with his tractor beam.