Hey, since I'm practicing resurrection techniques, thought I'd bring this up. There's lots and lots of add-ons for v-bulletin, why not see if someone either has, or can develop a "search" test as part of the registration process.
In essence, you give them pre-made tutorial with a sample question and see if they can find the answer by using the search button. If the system detects that they were successful then they can proceed with submitting the registration. Otherwise they'll have to retest successfully before proceeding.
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