Referral only registration

[rady]

Hey everybody, i was thinking about how this would be a very nice feature for any vb. Lots of boards are spammed by bots or trolls (i experienced this recently) and i wanted to add higher security to this matter. My idea is to have the already registered users generating registration links for new users, so nobody could create an account without a unique url generated by an active member. This feature will also keep an evidence of every member that invited new users and the new names created.

Any idea if this mod already exists or of its possible to be made?

my current version is 3.6.7