Getting scared by that exploit warning and all, I decided to upgrade my guestbook to the latest version.. the wrong way :\
What I did was upload the new files over the existing ones, of course, blanking out my current configuration.
Afterwards, I ran install.php but it would return:
Warning: mysql_connect(): Access denied for user: 'myusername_agbook1@localhost' (Using password: YES) in /home/myusername/public_html/gb/install.php on line 220.
So I manually edited the config.inc.php file, didn't work either and the guestbook kept returning Access denied errors.
Then I thought I might've been using the wrong user pass, so I deleted the user through Cpanel, added it again with a new password, and retried setting my guestbook up again through both install.php & the config.inc.php. Nope, Access denied errors all over.
I also tried deleting the complete directory, and adding a new guestbook directly and automatically through Cpanel, but it doesn't seem to be installing files on my server, not even create the directory. (Did I mention my host sucks?)
Argh. What a terrible friday morning.