Compare data in two columns and create a data on third column based on the comparison

Hi all,
I am trying to figure out this problem since a long time. I donot have a programming background at all and I hope someone helps.
I have data for 25,000 subjects. For instance:

A B
99 99
00 00
03 01
99 99
99 01

I want to create a column C which highlights or has a mark if there is 99 and 99 in both columns A and B.

Thanks
Shilpa