really easy way to get levels is to choose road on easy, build up normal defences (glue monkey is the key), around wave 15-20 start to build banana farms & upgrade them. Keep building up your defences, and before you reach wave 45 build a super monkey and upgrade to plasma, to handle the MOAB's, keep building super monkeys. You can easily reach wave 75 and have around 10000 bloons per wave.
Its funny how some games mean so much to people that they spend hours of their lives trying to better themselves in the game by hacking and cheating. It utterly defeats the purpose of playing fairly. If you want to hack something go to www.hackthissite.com where you can hack in peace and freedom.
I have to agree with Frogmanx, it is pointless to go to all the effort of making a really classy game like this then spoiling it for gamers by locking content. 1/5
 "No Time To Explain"){kind=icon}
 "Bloons Tower Defense 4"){kind=icon}
 "The Space Game: Missions"){kind=icon}
 "Starfighter: Disputed Galaxy"){kind=icon}
 "Amateur Surgeon"){kind=icon}
 "Farm Frenzy - Pizza Party!"){kind=icon}
 "Electric Box"){kind=icon}
 "Death Dice Overdose"){kind=icon}
 "Get Off My Planet"){kind=icon}
 "IncrediBots"){kind=icon}
 "Bloons Tower Defense 3"){kind=icon}