Sony Pictures launched legal action against Greg Strause and Colin Strause and the owners of Hydraulx Films on the basis that the latter had been hired to provide the special effects for the similar Battle Los Angeles (2011). Sony claimed that Hydraulx had not informed it that the company was working on a competing project. The case was later dropped.
The trivia item below may give away important plot points.
Wilhelm Scream: The well-known sound effect is used when Oliver gets grabbed by the giant walker and the soldiers are shooting at it. As it swipes the soldiers from the balcony, one of them falls with the Wilhelm.