They will verify with the homeland security agency and other such organizations if you appear to be in their databases.
Also they will verify with your current and past employers about the jobs that you performed.
Well one can write a book about back ground checking and what it includes. There is a full thread by Qorax about back ground checking which you must have seen. In simple words it can include
1) Education docs verification
2) Job verification
3) Name check
4) Police clearance
5) Security check
6) Travel history
7) Data base checking
8) Search through online websites liked "linkedin" or other online portals
9) If you have lived in Europe or North America or abroad, Address check through websites like "address.com" or 192.com
10) Authenticity of all docs provided if they are genuine from issuing authorities
They will verify with the homeland security agency and other such organizations if you appear to be in their databases.
Also they will verify with your current and past employers about the jobs that you performed.