I have s.17 in the EDOCS section too. Still looking for answers.
Please see this site
https://www.oic-ci.gc.ca/en/investigators-guide-interpreting-act
Related to the Access to Information Act these are exemptions taken by IRCC to withhold information.
Also see page 29 at this link
https://www.canada.ca/content/dam/ircc/migration/ircc/english/resources/manuals/op/op01-eng.pdf
5.27 Security screening of foreign nationals
Sections 15 and 16 of the Access to Information Act may exempt parts of the security screening process
from public access. Officers should read these guidelines in conjunction with chapter IC 1, Security and
Criminal Screening of Immigrants.
Security screening procedures identify persons seeking admission who are, or have been, involved in
espionage, subversion or terrorism, organized crime, war crimes and crimes against humanity. Note that
a security screening clearance does not mean applicants do not have a criminal record.
Officers are responsible for ensuring that persons who may threaten the safety and good order of
Canadian society are denied entry. Officers also help promote international order and justice by denying
use of our territory by such individuals. These goals are important, and strict compliance with security
screening procedures is required to achieve them.
Responsibility for responding to queries about delays in immigration processing rests with the
Department. Applicants or their representatives should not be referred to other federal departments or
agencies that assist in the security or criminality screening of applications.
Officers may refer to the background inquiries carried out by the Department, but specific details of the
process may be exempt from public access. No reference should be made to them explicitly.
Refusal letters should simply quote the part of the Act used to refuse the application. Officers need not
explain the security screening process.