I mean, if it's online it has a network/wireless card and a TCP stack along with at least some amount of RAM, so yea, in theory unless the programming is perfect it could be exploited. Now, it's not going to be used to run AI, but could very well get used in a DDOS or something like that.
I'm relieved my entire network consists of old computers and small, low power network devices. The only dedicated GPUs you'll find is discarded old junk in a cardboard junk box.
Being poor can have advantages :)