Suppose someone stated that for two years, they were unemployed and staying at home with children but were really making money doing porn webcams. Is this a blackmail issue since they never disclosed the porn business but misrepresented the two years on the resume and interviews?
Without knowing the ins and outs of the webcam porn and whether it was self employment, working for someone else) and how it was misrepresented, since not all employment is required to be listed on resumes, only what is relevant to the position, the answer can be both yes and no. If this was on an SF-86 then it is definitely an issue. If not disclosed during a security interview it is an issue.
It's not necessarily the porn business but the lack of disclosure that will be the issue. Although even if it were disclosed, if it is something you are embarrassed by and wouldn't want people to know about it, that would be another issue. If it's fully disclosed, common knowledge and wouldn't cause you embarrassment then it really isn't too much of an issue.