Well, maybe invite is the wrong word. More of a pop up thing that happened after he played Farmville and then took one of those silly quizes. He pointed it out, I looked, seemed harmless, no slimly stuff, I just didn't think anything more of it until now.
If he is doing the quizzes then yes, I would definitely get some kind of ad blocker. The quizzes (Which of Santa's reindeer are you? What Nightmare on Elm Street Character are you? kind of thing) are notorious for having some kind of pop-up or redirecting your to an advertisement. Also, if he is answering quizzes, then every once in a while you may want to clear out his applications.
To clean them out...
*Go to the "Account" tab in the top right corner
*Click on "Privacy Settings"
*In the bottom left corner click on the "Edit Your Settings" in blue underneath the words "Applications and Websites"
*In the top section titled "Applications You Use" it will say "Remove Unwanted or Spammy Applications" Click that.
*The list you will see from there is all of the applications (Farmville, Games and all of the quizzes) he has done. Go through those and click on the
X to the right of the ones you want to remove.
I don't clean out the ones I use on a regular basis (Farmville, Family Feud, etc...) You will be able to tell which applications he still uses and which he doesn't. It will have either "Last 24 hours, a specific date, or the words "Over six months ago" under each application to indicate the last time that particular app was used.
As long as those applications are still on his profile, he is subject to ads and/or pop-ups they generate. Also, until they are removed, the application can pull certain info of his.
I am notorious for taking the quizzes and have to clean mine out every few weeks. Not to mention, I do it to my kids' as well. Since they have to click the "Allow Application" in order to take the quizzes, every one of the quizzes/games/etc are listed. In going through the list of applications, I am able to make sure they are not taking quizzes I deem inappropriate and use it as an extra measure in keeping them safe on FB.
FB is such a fun thing, but can also be a little scary as a parent.