Today's term — a blend of kiddie and idiot — is synonymous with the older phrase script kiddie. In fact, kiddiot seems to have arisen as a shortened form of the phrase script kiddiot, although the latter is more often seen as script kidiot, as the earliest citation demonstrates:

"Microsoft is also painfully aware of the consequences of public disclosure of exploits as thousands of script kidiots attack vulnerable systems." —"Unix Security," Carole Fennelly, SunWorld, October 2000

For the record, here's an even earlier usage, although the sense is completely different:

"Maybe people have given up trying to keep companies from exploiting kids. After all, long ago, Saturday morning 'kidiot' cartoon shows became open season on tiny (future) consumers." —Ernest Tucker, "Song Deal Is Juicy for McDonald's," Chicago Sun-Times, July 6, 1993