User-id into /etc/passwd

[Paolo Consiglio]

Hi everybody,
I was looking into Fedora and I see a lot of user-id defined into
/etc/passwd file,
such as ftp, usr, and so on. It's seems to me they don't have access to
shell,
but I wonder if  that could be a problem for internet security...
Maybe can I delete them and leave only root and the standard users
without having any kind of problem?

thanks for answering, bye! P.