The omission of a common phrase

Botnets sometimes compromise computers whose security defenses have been breached and control conceded to a third party. Each such compromised device, known as a "http://en.wikipedia.org/wiki/Internet_bot", is created when a computer is penetrated by software from a malware (http://en.wikipedia.org/wiki/Malicious_software) distribution.

I'd like to know whether "have been" has been omitted after "control."
Thank you in advance for your help.