Trigger to restrict contact by last name

RestrictContactLastName

trigger RestrictContactLastName on Contact (before insert, before update) {

// Prevent updating or inserting a Last Name to the value of 'INVALIDNAME' in a Contact record

	For (Contact contact : Trigger.New) {
		if(contact.LastName == 'INVALIDNAME') {
			contact.AddError('The Last Name "'+contact.LastName+'" is not allowed for Contact records');
		}
	}
}