Comparison/conditional formatting of two columns

[Christ143uk]

Hi,

So my problem is:

I have a list of 1 million rows of phone numbers
I have a list of 500,000 phone numbers
In both of these lists phone numbers are repeated so I cannot use conditional formatting to highlight duplicates.

Basically I need to highlight any phone numbers/rows in the 1 million lines that also appears in the list of 500,000 phone numbers at least once.

Thanks in advance

 

[Fluff]

Assuming both lists are in column A.
Select A2 to last row in A & use this CF formula
=ISNUMBER(MATCH(A2,Sheet1!A:A,0))
change the sheet name to suit