I'm just curious if new version of backtrack Kali be hacked like back-doored or crack user password like the windows or mac
Yes, it can be hacked. No OS (outside of some limited micro kernels) has proven perfect security. It is theoretically possible to do, but nobody has done it and even then, there would be know way to know it is implemented after the proof without building it yourself from the individual circuits on up. It's not possible to know if there are any active backdoors for sure since they could be subtle, even encryption could possibly (though unlikely) have a back door.
Outside of encryption, with physical access, any system can be read directly off the hard drive and configuration information can be replaced to simply change a user. If encryption is used and the encryption itself isn't back doored (and is properly implemented) it should require the password to access even if there is a backdoor in the OS itself. (The password should be a key piece of information for generating the actual decryption key.)