Last Years Open Source - Tomorrow's Vulnerabilities

Linus Torvalds, the creator of Linux and Git, has his own law in software development, and it goes like this: "given enough eyeballs, all bugs are shallow." This phrase puts the finger on the very principle of open source: the more, the merrier - if the code is easily available for anyone and everyone to fix bugs, it's pretty safe. But is it? Or is the saying "all bugs are shallow" only true for