He would have to look a 264 combinations.
This is because:
2 letter words =
AA to ZZ
AA to AZ is 26 combinations, then you repeat with BA to BZ, CA to CZ etc.
As you repeat this 26 combo thingamajig 26 times,
This means that there are 262 combinations for two letter words.
3 letter words =
AAA to ZZZ
AAA to AAZ is 26 combinations, AAA to AAZ is 26 combinations.
then you repeat with ABA to ABZ, etc.
This means that there are 263 combinations for three letter words.
4 letter words =
AAAA to ZZZZ
AAAA to AAAZ is 26 combinations, then you repeat with AABA to AABZ, AACA to AACZ etc.
This means that there are 264 combinations for four letter words.
Not sure about the answer though...