Where is defined " XXX unauthorized file extension" message

[Miroslav5]

Hello, I restricted some types of file extension in sys properties. So now, when you try to load attachment with restricted file, it shows message " XXX unauthorized file extension". 

My question is, where is this message defined, need to translate it. I tried UI messages but was not successfull.

Thanks guys

[Miroslav5]

Unfortunately its differetn message. The message is " exe is not authorized file extension. "