I have an issue here with users stealing internet via apps like Freedom and HTTP injectors.
AFAIK they can do this because mikrotik hotspot allows DNS requests for unauthorized users

Any solutions?

This is a reply from mikrotik support
Hello,

You can add firewall filter rules that drop DNS requests to your router. You can learn how to configure firewall rules from this wiki page:

https://wiki.mikrotik.com/wiki/Manual:I ... all/Filter

Best regards,
Martins S.
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My question:
I have a Hotspot running. If I drop all DNS requests clients will not be able to resolve the hotspot portal address!