UltronUltron-6 was the iterative version of the Ultron AI which was uploaded before Ultron-5's physical form was destroyed.

Ultron-6 was transfered to another Ultron body, this one located in the armory at Stark International in NYC.  Ultron-6 invaded and took control of advanced weapons systems everywhere.  In order to destroy the Avengers, Ultron-6 took control of all of Tony Stark's old suits of Iron Man armor, and used them to attack the Avengers at the Avengers Mansion, while he himself attacked the SHIELD Helicarrier to drain the access control codes for the SHIELD nuclear arsenal from Director Maria Hill's mind.

Ultron-6 shut himself down once Hank Pym uploaded a data set which proved that Ultron's AI was based on Pym's own brain waves, making him just as much of a chaotic problem as mankind.