Primary adamantium version (in case you were wondering)

Sure Ultron is strong enough to backhand both Thor & Wonderman simultaniously, and his energy blasts have Knocked them around or out as well but we've never seen anything graphically impressive from Ultron. I do think 6 blasts from Ultron will register on thanso though. I don't think that Thanos's blasts will effect Ultron. I do think that Ultron will resist any type of 'versitily' power that Thanos might use (as they're not his area of expertise). If thanos has one sided prep of course he wins, without it though I think his best bet is to try to evade the Ultrons long enough to produce a virus of some sort.

Oh for the record the only person who's managed to take over Ultron's programing is Dr. Doom. . . once when Doom has one sided prep and was specifically gunning for Ultron (and had Namor do the actual deed or placing the device on him) and secret wars where Ultron was deactivated at the time (thanks to Molecule man & Galactus). Ultron tech as proved superior to shield tech, pym tech, stark tech and the Phalanx tech in the area of programming . . . of course thanos is a different story just wanted to defend my boy and mention that not just "anybody' could break him with a virus.

Only Drax the Legend can quote Drax the Legend. NT · Drax the Legend

And this was the Hulk before the healing factor was introduced and the Hulk simply had high-invulnerability.

Ultron was always presented as team-level threat. One Mark-17 Ultron would give Thanos a tough fight. 6 of them on Thanos would put a mad hurting on him.