I am aware that there already are some questions regarding on how to implement field level permissions customization in SharePoint, such as:
Most of their answers either say that it's impossible, either provide a user interface or dependent list configuration. Recently, I've read the following article: 3 Approaches to Restricting Access to SharePoint Columns and Metadata. The author wrote there:
The third option is to write custom code that enforces custom business logic for data access.
There are third-party solutions out there that address column-level security scenarios. Most (or all) of them use one of these approaches: conditional formatting, custom content controls or forms, related lists, or “middle man” injection into the content access processes of SharePoint.
I am aware that third-party SharePoint add-on providers, such as KWizCom, offer solutions which allow such field level permissions customization. Once hidden, a SP list field cannot be retrieved even if the user tries to use the web services API, MS Access or some other data access technique.
Since such goal is clearly possible, but MS doesn't provide any documentation on how to do it, could you provide some resources/hints about how to develop and implement such a customization?