Sessions question

Hi All,

I was wondering if I could ask a "general" question:

Looking to add "logged on" status' to my CGI scripts. And every Perl book I
have refers to "Sessions". Perhaps I am skipping over something major here,
because my question is this:

Sessions appears to be about storing the "session #" in your cookie. But
how is that safe? I mean cookies are viewable, and therefore a session id
can be copied and ported to another computer.

Mind you, I am not storing credit card type info, but still, I would like
some semblance of seurity here.

I am missing something? Is there more to "Sessions" than I realized?

Thanks.

Daniel