Secunia Research classifies vulnerabilities by rating the severity of vulnerabilities from 1: "not critical" to 5: "extremely critical."
Going by the PR Heartbleed received, you would be excused for thinking that what we were dealing with here was, indeed, "extremely critical."
But it was not, as vulnerabilities go. That rating we use for "remotely exploitable vulnerabilities that can lead to system compromise. Successful exploitation does not normally require any interaction and exploits are in the wild."
The Heartbleed vulnerability was in fact only rated as a 3 of 5 by Secunia: "moderat