With blackmail and fraud convictions (and a 3-year prison sentence behind you), I would hope that nobody would give you a job with access to systems that enable you to get at personal information or money. That's their business, of course; but they'd presumably be exposed to an action for negligence if something went wrong as a result of them employing someone with that record.

Blackmail and fraud are both offences that involve using others as means to ends, and require the ability to discount the damage and pain you cause to others. If I were hiring a coder (let alone a computer security consultant) I'd search for a long time before hiring someone with a record of that kind of untrustworthy behaviour.

Sorry to be blunt; I know that some companies pay good money to convicted criminal hackers for their expertise. But I think that's a deplorable practice; it encourages the view that hacking/cracking, blackmail and fraud are a sensible route into regular employment. I think those convictions should be a blocker.