[Princeton]

You do not need a hack to accomplish what you want. You can prevent a group from viewing threads created by others using vb's default permissions system.

If this is not what you where asking there is no need to continue reading.

For example, if userA, who belongs to groupA, creates a thread it does not mean that userB, who belongs to groupB, will have access to view the thread. (vice-versa)

You control this by setting permissions to specific usergroups for specific forums.

The usergroup section in your vb cpanel will allow you to set DEFAULT settings permissions per group. However, you can change the permissions per group/ per forum by going into the Forums & Moderators / Forum Permissions and modify permissions for each group as you see fit.