! password in /etc/shadow

[James Scott <jayscott0@gmail.com>]

I am attempting to configure a package that is instructing me to
assign a password to the user account of a different package.  I am
new to Linux, so I am a little afraid as to what affect this might
have on my system.

When I look at the /etc/shadow file, the password field is currently
an exclamation point (:!:).  I understand that an asterisk (:*:) would
mean that the account is disabled, but what does the exclamation mean?

Also, if I assign a password to this account, and it breaks the other
package, how can I change it back to whatever the :!: is?

Thank you,
J.Scott