You may be lucky, you may be an unattractive target, you may have been infected without knowing and be an unwitting DDoS gateway.
Computers and programming was all about solving problems for decades. Few could afford the early computers and far fewer would have thought about abusing them and had little chance not to be discovered when they did.
That implied that software did its best to compute valid outputs for valid expectable inputs, nobody tested for seemingly nonsensical trash being entered as input. But that's exactly how you overwrite stack data and hijack the control flow via
return oriented programming or similar. And finding out exactly what you need to put there is easy and automated, if you have a binary copy of the exact same binary code at your disposal, which is easy with software widely distributed in binary.
You should read that up, it's a true marvel of (criminal) ingenuity! And it's been made so easy, even half-dumb kids can do this. They simply need to write the malware code and they can use a special compiler to translate that into data inputs you need to feed the victim to hijack it with that code.
Fixing that in seven decades of old code is tons of hard work that is hard to finance, because it doesn't help the original use case (e.g. doing your accounting). So lots of time it just doesn't get done and software contains vulnerabilities. As long as nobody knows about them, it's relatively safe. But once they are found and documented, they either need fixing or they turn any system not patched into a wide open potential bot. And those are permanently scanned for, found and exploited by professional mafias and inimical state actors.
And even writing new code that is inherently safe isn't exactly easy or 100% reliable, even if the industry is trying very hard to enable that e.g. in the old days via ADA, SPARK, formal verification, or more recently via programming languages like Rust or ISA extensions like CHERI, ARM tagged memory or x86 shadow stacks.
The Mirai botnet was able to spread to millions of devices exactly because they had unfixed known and documented vulnerabilities which made malware automatically hijack them and turn them into a bad actor.
Since many of these devices could not be patched, some "white hats" actually went ahead and bricked them. Now the legality of that hasn't been decided in courts and those might even contradict each other, but I'd say as an owner of such a device you would be legally responsible for part of the damage that you cause by allowing it to be abused (obviously the abuser and the vendor share some of the guilt).
You know Windows 7 is no longer maintained so if a hijacker turns your Windows 7 machine into a bot, that is a consequence of your action (or inaction in this case), which implies liability.
Even not knowing it's unsafe to leave loaded guns or grenades littered around your house, doesn't mean you're not responsible what happens if a puppy, a kid or even an intruder plays with it. And in this case you've been told, even if you didn't listen.
I'd suggest you spend a little less time laughing about it or shrugging it off and investigate.
Sure, computer security is a billion dollar business and there is tons of exaggerations and FUD around. But unlike genetic code computer code does not mutate and manage that variability on every single device. The fact that on millions of devices the code is truly identical to something you know how to kill is too attractive not to exploit by digital predators of any persuation.
You might also want to add
Krebs on Security to your daily reading list.