Theory about Ultron's origins in Avengers: Age Of Ultron

In SDCC it was finally revealed that Ultron will be the enemy in upcoming Avengers sequel. It was however surprising that Joss Whedon comfirmed that Hank Pym, a.k.a. Ant-Man, would not appear in the Avengers 2, even though he is coming to the MCU in phase three. Ultron was in comics Hank Pym's creation, but in there has already been rumors that this robot menace would be Tony Starks handwork in MCU. This made me speculate about the robots origins; and I came up with two possible theory:

1) One of the questions with Avengers sequel is that if Thanos is involved with the plot in any way, if so; could it be that he causes Ultron's birth by corrupting, with some kind of cosmic virus, one already existing artificial intelligence in MCU: J.A.R.V.I.S. I know that this might first sound a bit absurd, but when you remember that in the end of Avengers there was tons of Chitauri-technology left to Earth, it might be that the virus comes from them without Thanos being directly involved. The virus could be some short of defence program desinged by Thanos in order to make sure that his enemies could never get any benefit from his army's gear. Invloment of J.A.R.V.I.S. would also be logical when in comics one of Ultrons first plans to destroy Avengers involed Jarvis being hynotized to work against the heroes.

2) Second theory would involve the ending of Iron Man 3. Many have wondered if Tony still wanted to be Iron Man after what happened at the end. It could be that Ultron will be presented as something that Tony has desinged to replace Iron Man in the team. Tony had self moving Iron Man armors in Iron Man 3, add the self conscious and tadaa; you got yourself an Ultron prototype.