A former member of the hacker gang Kryogeniks was sentenced to four months in prison Monday for his role in a 2008 stunt that replaced Comcast’s homepage with a shout-out to other hackers. James Robert Black Jr., 21,was known as “Defiant” when he and two other hackers hijacked Comcast’s domain name in May of 2008 — a prank that took down the cable giant’s homepage and webmail service for more than five hours, and allegedly cost the company over $128,000. Visitors to Comcast.net had been redirected to a simple page reading “KRYOGENIKS EBK and DEFIANT RoXed COMCAST sHouTz To VIRUS ...