Hello!
I used to have a series of verification questions in my 2.0.x forum and those proved to be very effective in preventing spammer registration. However, after upgrade these are gone and I cannot find them in the settings.
In 2.1, the settings can be found at Admin -> Configuration -> Anti-Spam. I'm not sure why they would disappear during the upgrade though. In the database, they should be in the "qanda" table.
Strange. I cannot find any "Anti-Spam" settings.
Edit. found them. Turned out to be a bit mess because of language settings after upgrade.