I have some ideas to expand your addon. Could you implement them? That would be perfect! I can do this all myself of course, but have no time currently.
1. Let the plugin set 1 option at the top:
$membersRule=10; //defines amount of posts, which registered member should have in order to bypass the addon rules. Setting to 0 disables checking of members.
All guests should be automatically (without any option) be applied to the addon rules.
2. Let the addon use an external dictionary, let's say, addon_anti_guest_dict.php, which contains $anti_guest_wordlist; in this array, you may define any possible word, which needs to be prevented in user postings. You can take the dictionary from old Flood Filter addon.
You can keep the URLs rule additionaly, for displaying two different kinds of warnings. If user has typed something related to URLs or emails ('@' sign) - this is what currently $anti_guest_terms has - but it's also needed to prevent guests from posting email addresses, too - you display the error like current. "Because of spamming issues, you are not allowed to post outgoing links, URLs or email addresses." If user has typed a forbidden term from dictionary - the warning should be "You are not allowed to post the term '[WORD]'".
3. $anti_guest_title and $anti_guest_msg should be separated in language pack.
Let us know what do you think.