Just a single box? It's definitely a scam.
What does a Million Dollars weigh?
According to 419 letters, the security vaults of dozens of African storage facilities are jammed with boxes packed with millions of U.S. Dollars. The average amount stated is around $25,000,000.
Assuming that the Dollars have all been changed into $100 bills, $25,000,000. equals 250,000 - $100 bills.
A pound of U.S. currency notes, regardless of the denomination, contains 454 bills (Avoir du Poids system. Troy system is 375 bills/lb.*). That runs to a little over 550 pounds of money. Provided we're speaking of $100 bills, which are not that handy in 3rd world countries. The standard denomination is $20 bills.
Using the above calculation for $20 bills, we would be looking at 1,250,000 pieces of currency at close to 2,800 lbs., or over 1-½ tons of money.
American currency is 2.61 inches wide x 6.14 inches long x .0043 inches thick*. A standard box is 12x12x16. Packed in the most efficient manner possible, one would need at least 330 boxes to house $25,000,000.
The next time you receive a 419 letter asking for help in retrieving vaulted currency, you will know what questions to ask.
http://www.fraudaid.com/ScamSpeak/Nigerian/419_Hidden_Facts/what_does_a_million_dollars_weigh.htm
As a baiter I love asking about the shipping weight and size of the trunk full of money. It's fun to watch them squirm trying to come up with a believable number.