A buffer overrun happens when writing data past what is the expected memory space in an array — as a computer science topic. Of course you would need to understand, how memory layouts work in your computer, how and why data is written and in what particular context, and much more. I don't want to write an essay that you may need even more abstract contexts to even understand so I'll be brief. You wouldn't often notice a buffer overrun occurring because writing to memory outside of the expected space doesn't usually cause hard crashes (unless you are debugging for them) but instead affects data in other parts of the program. For example if you accidentally write past the end of a string (that's just text stored as data btw), the string might still say, "Hello World" but if the data you were using for your player's health is placed right after the string in memory, suddenly the health data has been written over and now your player has -2147483648 health (not specific this is just an signed overflow joke). Memory (heap in this case) corruption is NOTORIOUSLY hard to detect, find, and fix. I'm assuming the library that doesn't happen to exist on Win7 which is missing is for safeguarding against, or detecting accidental corruptions due to buffer overruns. And before you ask no, this is not corruption as in, file corruption on your drives or anything, this is memory corruption which happens all the time in programming, usually do to an oversight in code. It's only a temporary space and more often that not your OS can and will prevent a program from altering memory outside of it's space *accidentally*. As for your "giant red flags" about it going through testing. You can't test every single machine and environment those machines are running in. In this case, the bug (technically missing library they linked against so not really a bug but more of an oversight) very likely wasn't found on any configurations that they tested for. (I should also mention that if it relys on libraries from the OS, changes to the OS like updates could also break functionality for the game which wouldn't be Bungie's fault at all) And no, it's not easy to just "test everything". If you understand that you are lacking knowledge on the subject, maybe consider learning more about it. Computer Science is actually quite fun when you start to understand the concepts!