I remember, ~20 years ago, there was some free Christmas elf game (Flash?) that went viral and everyone was playing it. Struck me as a perfect vector for malware, I was a little surprised that didn’t happen.
All our network traffic was unencrypted, which enabled all kinds of shenanigans until the security culture seeped into corporations and the public.
When stories talk about time travelers that hijack old technology instantly, it makes complete sense. Someone with modern hardware, software, and knowledge could completely break most technology back then. They better not forget their modem, though.