4.2 KVM vnc connect need password?

[ma y]

Hi,everyone.
My environment :Cloudstack4.2 + centos6.4(KVM).
When i use vnc viwer connect a VM,type "192.168.1.100:0",it shows need a
password to continue.
Is that a new feature for KVM vnc ?  How can i use vnc viwer to connect it
and what that "password" is .
thk you !