I wasn't saying I'm sure account A infected files on account B. That's what the guy I was responding to seems to believe, that the exploit occured due to a badly written PHP script. It's more likely that it was the PHP server itself that had the exploit, or something else entirely at the website.
I'm not blaming Linux at all, nor is that what my argument is. I'm just saying that exploits can occur regardless of operating system, and just because you're on Linux does not necessarily mean your machine will not get compromised. Often, it happens because of an app, NOT the operating system. Therefore, one should blame the app, NOT the operating system. Sometimes, the OS does something stupid that allows the app to fuck up when it could have easily stopped it, and then the OS is to blame. (Not saying this was the case in my situation). However, whenever an app has an exploit in Windows, people automatically blame Windows, regardless of the situation. Whenever an app has an exploit in Linux (as was the case in my scenario), well...you could tell how everyone jumped and said it MUST be my fault, or not my fault, then the php's script's fault, and if it's not the php script's fault, then the PHP server's fault. It could never, ever be Linux' fault.