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XBox - Black cheats

Unlock Black Ops - Finish the game on the hard mode
Unlock M16A2 - Finish the game in the Black Ops mode
Unlock Silver Weapons - Finish the game in either the Normal or Hard mode

Unlock BFG /M249 SAW/ in City Streets level:
Go to profile name option and enter 5SQQ-5THA-ZFFV-7XEV as your name. 
Note: Always include the "-" symbol when entering the code.
After entered, press "Done", you will be able to re-enter an actual profile name. 

Alternate profile names:
9NDH-293Y-P6MJ-829Q 
EG4P-ZGUJ-6SQJ-3X68
FG6S-WFZG-7MDP-PZGT
G68Y-X5LB-N8PE-9D7N
HQ6G-ZP3B-C5LE-WMXA
3K67-9J5G-NSQH-G49M 
3ZEQ-JXH9-TR2H-Y87D 
5Q9E-4SEK-FJVV-C5HV
6DEG-7W3X-RKJF-TDF4 
8PPV-J8SY-KA8T-BPYK