Counting based on three criteria

Okay I didn't exactly know how to phrase this, but what I want to do is to check to see if SCC in Column C are in DRCC based on what security they have (column B) on the attached sheet.

Column A is basically assigned to a person with security 1 (or 2 or 3) and all of these numbers in column A should be in column C - if they aren't I want to know (or count '0'). I've been wracking my brain about this and I can't crack it yet.

As an example:
Someone with Security one has the following numbers in column A:
1212000
1212400
3480368
1212400
They NEED those numbers in column C - however column C has these numbers:
1212000
1212400
3480368
3480372

So column A is missing a number. I don't need to know what that number is (3480372) but I do need to know it's missing a number.
The reason I don't need to know the precise number is because it's possible that there could be several numbers missing. Also, the number of rows and numbers are completely variable, some security will have only 1, others will have a dozen.

That worked!