This answer is given many times, actually what are Security checks performed after medicals. This is taken from the offical web site of csis for your knowledge....
What is security screening?
Security screening is a process by which the name of a security clearance applicant is verified against CSIS databases to determine whether the applicant is mentioned in relation to threat-related activities. Depending on the level or category of security clearance required, security screening can also involve interviewing the applicant's friends, neighbours and employers, consulting with local police, and possibly interviewing the applicant.
There are three levels of security clearance as defined by the GSP: Confidential (Level I), Secret (Level II) and Top Secret (Level III). The level of security clearance required is determined by the need for access to classified information or assets in the performance of duties associated with an individual's employment. Level I and II security clearances involve checking CSIS databanks. Level III security clearances require a full field investigation, which involves checking CSIS records; interviewing friends, neighbours and employers; consulting with local police; and, possibly interviewing the applicant.
What is security screening?
Security screening is a process by which the name of a security clearance applicant is verified against CSIS databases to determine whether the applicant is mentioned in relation to threat-related activities. Depending on the level or category of security clearance required, security screening can also involve interviewing the applicant's friends, neighbours and employers, consulting with local police, and possibly interviewing the applicant.
There are three levels of security clearance as defined by the GSP: Confidential (Level I), Secret (Level II) and Top Secret (Level III). The level of security clearance required is determined by the need for access to classified information or assets in the performance of duties associated with an individual's employment. Level I and II security clearances involve checking CSIS databanks. Level III security clearances require a full field investigation, which involves checking CSIS records; interviewing friends, neighbours and employers; consulting with local police; and, possibly interviewing the applicant.