Are you speaking about scenarios that could happen ? or there is an actual threat going on, because I don't understand why It became suddenly important to verify signature while we didn't see such a thread in the past.
Wondering too.
Cobra made an alert on bitcoin.org:
https://bitcoin.org/en/alert/2016-08-17-binary-safety but no one knows why he did it and what he means by it. So right now now the assumption is that something nasty have been compromised, but there is no proof of any such compromise yet.