This is a perfecr example case for considering an enterprise, professional world class Open Source ERP solution like OpenERP, ERP5 or Compierre which will not only allow "user" modifications and configurations to application functionality/ source code/ to suit purchaser's needs and requirements, but will generally work with far better with all other data formats and APIs, and is especially beneficial for evading all the proprietary vendor lock-in and incessant hands-out for more payments as article writer noted. If the company has fairly competent personnel in their technology support department, it would not be climbing Mt. everest to have them acquire programming knowledge and expertise from the FOSS applications developers, at considerably less costs that custom modifications. That is unless the company technologists are extricably tied, by perks,limited training and/or personal incentives to Oracle, Microsoft or other large proprietary software vendors whi derive much of their great profits from just such scenario as described in the article.
Since Ubuntu Linux and most every other Desktop Linux available in 2014 has an "easy to use", intuitive GUI firewall configuration utility, I an skeptical that any person using Linux, even for the first time would (a) receive space on Slashdot to ask such question, and (b) a question that I consider completely unnecessary if writer is guided by common sense in using the standard and well documented visual Ubuntu Firewall application, and suspiciously naive in not going first to Ubuntu Help center or any person nearby who is not simple-minded in regard technology..