VBA for finding duplicate values in 4 columns? #Stumped

Hi Excel Masters,

I'm trying to find some code that allows for duplicate values to be highlighted across a hundred thousand rows of data.

The data is filtered down on four companies (A-D) that each contain the same group of states that I'm filtering down on. Attached is an example of what I'm looking for where Excel will highlight the information that is identical in columns C and D. The code will then go through each of the entries in Column B's filter and highlight the duplicates in C and D.

Anyone able to help with this? Thanks!