what does cms dialer do?

what does it do

It protects you against USSD attack. It’s a fix for a vulnerability in Samsung phones which can wipe the whole mobile clean. Always select CMS dialer when you get the message just to stay safe.

then maybe I am wrong in how I thought ussd attacks are sent. so how are they sent

Some phones, anyhow. As previously pointed out, this is a non security issue with my phone.

how are ussd attacks sent

I don’t experience the USSD attacks when using Opera as my browser. But it does come up when using the default browser. Basically it throws a pop-up that props you to dial a code that would expose your phone IME number and other vital information and it could wipe your phone etc. Here’s detailed info on USSD attacks: 'Dirty USSD' Hack Wipes Samsung Phones. Is Yours Vulnerable? | PCMag