Posted this over on /r/SecurityClearance and someone asked me to post it here because we've been getting a lot of questions related to people being coerced into lying/omitting information on their enlistment paperwork by recruiters and how it will come back when they need to get a clearance either in the military or when they leave to become a contractor or a government civilian.
As stated on the second page of the SF86:
The U.S. Criminal Code (title 18, section 1001) provides that knowingly falsifying or concealing a material fact is a felony which may result in fines and/or up to five (5) years imprisonment. In addition, Federal agencies generally fire, do not grant a security clearance, or disqualify individuals who have materially and deliberately falsified these forms, and this remains a part of the permanent record for future placements. Your prospects of placement or security clearance are better if you answer all questions truthfully and completely. You will have adequate opportunity to explain any information you provide on this form and to make your comments part of the record.