Heartbleed, a long-undiscovered bug in cryptographic software called OpenSSL that secures Web communications, may have left roughly two-thirds of the Web vulnerable to eavesdropping for the past two years. Heartbleed isn't your garden-variety vulnerability, so here's a quick guide to what it is, why it's so serious, and what you can do to keep your data safe.

Conceptually sure, but in this particular case it wouldn't have helped. The vulnerability didn't corrupt memory such that free could have detected it, it simply wrote memory out to a socket.

Why not? For example, the OpenBSD malloc (with the G option enabled) may place guards around each allocated block which would prevent this exploit from reading outside the allocated memory within the same application as it would trigger one of the guards and cause a segfault.

The problem here is that rather than using the system malloc/free, it keeps its memory cached to reuse it. Hence why the guards are ineffective.