What exactly is a mathetmatical proof? From this question it's clear it doesn't require any special symbols.

From a question on another sites

[Computer] Viruses have no “cure.” It’s been mathematically proven that it is always possible to write a virus that any existing antivirus program can’t stop." [0]

[0] Secrets & Lies. Bruce Schneier. Page 154

In these contexts what does it even mean to be mathematically proven? Does it just mean logic was used?