Quote: "It's easier to find exploits in open source software, obviously"
It may be easiER but it isn't that difficult to find flaws in closed source applications to begin with. Windows for example - hackers rarely find flaws themselves and actually reverse engineer the patches designed to fix them (so if the issue is identified internally, reverse engineering the patch that is eventually released allows determination of what exploit can be used on unpatched machines)
Also I think with modern static analysis, fuzzing and auditing it's not so common to see purely in-code flaws like overruns: often it's the configuration data or the way its used in combination with some other service that poses a greater risk
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