Hello,
In an nutshell...Under admissibility they check the credibility of the applicant their PP etc with international organizations database like Interpol etc...
The Canadian organization involved in this- https://www.csis-scrs.gc.ca/index-eng.asp
Go through with some links to get some over view http://www.canadavisa.com/immigration-security-clearance.html
Qorax words:-
Security & Criminality Checks:
A part of the b/ground checks is the 'Security Check'. It commences after our med results are submitted to the CHC. This is a major activity -mainly concerning our 'safe inclusion' into the Canadian Soil; vis-a-vis, Political, Socio-Econmical, Anti-Social disposition, perceived Threat to Canada's integrity etc. This gets us the SDEC, CDEC & SECCRIM.
This is a serious & time-consuming stage, involving many agencies, including CSIS, Interpol, NASC, Database Checking & touch-base with Local Police. Many things are considered here... the No. of countries visited, Applicant coming from 'certain' countries, ex-Servicemen [including Law Enforcement services], Prolonged stay in a country w/out sufficient docs to prove cause, frequent traveling to certain nations, your *Name (?), Inter-Religion/Nationality Marriages etc.
If everything is simple & straight, the file soon gets into the 'final review' stage. If there are any 'red flags', our case goes into a 'spin'. Then our file might go to the local Police/CID agencies; the outcome/timeframe of which is beyond the control of CIC. And thereby the timeframe can be anything [sometimes beyond 1yr]. But, usually this stage should be over by 5 months max. However, a point to be noted is that we can also be called for an Interview [at this stage], due to this reason.
-Culmination: Only upon security clearance we receive the PPR.
-Timeframe: Around 2-6 months. Avg. 3 months. [With new system, sometimes PPR is clubbed with Meds]
-eCAS: Still 'In Process', but 'Med Results Recd.' inside.
*Yes, that's how a certain Mr. Sharukh Khan was detained for 4.5 hrs in an US port. He was a VIP, thus 4.5 hrs. For u & me -things could be different.