Dildog was Scott Adams' original name for the Dogbert character in the Dilbert comic strip. No doubt worried that editors would object to the prurient substring, Adams changed the dog's name before submitting the strip for syndication.
DilDog is a fairly well-known Boston-area hacker (of the kind that likes to find holes in security software) and member of the Cult of the Dead Cow and the L0pht (now @Stake). Principal author of such fine software products as the Back Orifice remote administration tool and the "award-winning password auditing and recovery tool" L0phtcrack. A fine, congenial fellow; a glass or two of 10-year-old Laphroaig is a good way to get him talking about the interesting stuff. His handle is indeed derived from the Dilbert character, with the second D capitalized after he was laughed at too much for having "dildo" in his name.