Private tertiary institutions holding on to pin codes meant for registration by prospective national service personnel have been warned they risk prosecution.The National Service Secretariat says it has received complaints some institutions are holding on to its registration pin codes as a means of getting students to settle their bills before completion.Others have allegedly extorted money from the students calling it registration fees.But Executive Director of the NSS, Vincent Kuagbenu, says the act is not only proper but also warned that institutions who are caught in the practice would be punished.