Here is the link to the VB mod
For our scope, the "cookies" mode is comfortable. No need for "IP/ Database Logging"mode.
While for "drive more registration" alert the second option is requested:
This plugin offers two options which can be used to drive in more registrations. The first option allows you to show a reminder message or advertisement after a guest has viewed a certain number of threads. The second option puts up a roadblock stopping guests from viewing threads altogether after reaching a certain number of views. Both options work together to encourage and ultimately force anonymous visitors to either register or login but can also be used separately based on your individual needs.
The "stop" message must be a phrased/customizable template.
50$ donation to the coder.