Groups running wild

[kwhiskerz]

I have noticed differences in /etc/groups lately.

Older files had the form group:*:
Newer files have the form group :x:
On my laptop yesterday, a groups.rpmnew was created with the form group::

I read the manual and it suggests that the latter form means no password.

What does all of this mean? What effect does the * or x have? If it is blank, 
what does it mean for a group to have no password? No password for login? Why 
would such a file be generated upon yum update for my laptop?

Can one have different settings for different groups in the same file? When would 
one use which setting?
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