Try this:
There is a bus with 7 girls inside,
Each girl has 7 bags,
Inside each bag, there are 7 Big cats,
Each Big cat has 7 small cats,
All cats have 4 Legs each!
Question: How many Legs are there inside the bus?
The total number of Legs would be the password for the attachment.
If you can't open the file, the answer you obtained is wrong.
Happy trying !