Obviously the two are related. But they are also not much frequented. So my question is whether we really need them both. I'd say remote-ussd-attack (x2) could easily be referred to using ussd (x1) and security, so I'd suggest to make
ussd the main tag, merging
remote-ussd-attack into it and make the latter a synonym to the former.
While waiting for your opinions (or quick actions, if approved by our dear moderators), I meanwhile go tagging the other USSD related questions -- so please don't wonder if the mentioned numbers have changed :)
EDIT: Yikes, there's also the dialer-codes (x13) tag to be considered. Are USSD codes to be classified as "dialer codes"? Should that be the merge-target instead?