Past tense and past participle of disown. Refused to acknowledge as belonging or pertaining to oneself. Denied the ownership of or responsibility for. (from Random House College Dictionary)
"Disowned" also refers to the state of a computer system that a cracker had once compromised (or "0wn3d") such that the computer becomes secure against the cracker's repertoire of techniques. This involves patching the operating system and any running services against vulnerabilities that result from bugs in their code. See also computer security.