Keep in mind worm deployment (even "good" worms) is illegal and has a history of causing more damage than good. http://en.wikipedia.org/wiki/Computer_worm#Worms_with_good_intent
Apparently, he modified some worm code to fix a BIND problem, then search out more unpatched systems to infect and fix.
Someone named Markus Kern gave out some interesting IIS code in 2001, during or just after the "Code Red" worm epidemic. When the code got a "Code Red" signature, it would propagate itself to the IIS server from which it had received a "Code Red" signature. See: http://seclists.org/vuln-dev/2001/Sep/1
Looks like one "Herbert Hexxer" did something much the same: http://seclists.org/vuln-dev/2001/Sep/0
It would be interesting to hear if anyone fixed Markus Kern's code and released it into the wild. "Code Red II" worms were an ongoing annoyance for a couple of years, then suddenly and instantly disappeared.