This is their entry on the Marvel wiki.
The Hydra Four were Hydra versions of the Avengers sent into Manhattan to cause havoc in an attempt to draw out the Avengers. Only Militant fought his counterpart (Captain America), and although he held his own, he was ordered to retreat, along with the other three.
Spider-Man later infiltrated their headquarters, where it was revealed each member has received altered genetics, explaining their strength and abilities.
From – Amazing Spider-man Vol. 1 #519
