Earlier quoted context omitted.
If you hide it you risk being discharged a month, a year, or five years from now when your employer finds out, and then they aren't referenceable. If I were hiring for a security-related job, I'd consider the poster if he not only disclosed the conviction, but also contextualized it on his cover letter the way that he did in the pastebin, and if he provided some character witnesses (teachers, employers).
"If you hide it you risk being discharged a month, a year, or five years from now when your employer finds out, and then they aren't referenceable." This, this, a million times this. It's not even losing the job that would be the worst for me, it would be the paranoia of turning up to work every day thinking "Did they find out about that thing now? Are they considering firing me or did they decide it didn't matter? A…
Everything you have said on the Internet, ever, "could lead to dismissal". It's a risky world. You just gotta make the best decision you can at each point in time.