McAfee recently reported over 75 million new malware samples detected in 2011. This number, while shocking, no longer matters as an absolute value. It also highlights a glaring flaw in network defense philosophy.

First, this number is only calculated from all detected hashes. Any changes in the binary results in a new, unique, hash. This means that only a small change by the adversary is necessary to effect a “new” piece of malware. A simple thought experiment: if there were 75 million malware samples, each with only one byte difference between them – this method would count 75 million “unique” pieces of malware.

Second, the number alone says nothing about the threat environment. It does not illustrate the attack vectors, vulnerabilities, or exposures used by the malware; nor does it describe the danger or effectiveness of the various malware samples. Maybe there is only one piece of malware and it’s 75 million varieties are all harmless. 75 million is now a very large number signifying nothing.

However, it does matter as a relative value showing the number of unique samples over time. For example, in 2007 unique malware samples rose 565% from the previous year [from A Brief History of Malware]. The velocity of unique malware samples detected in the wild (or the slope of the line if you prefer) is clearly increasing.

Why? It means that malware authors and operators are exploiting the primary network defense practice: default allow all – the black list. Defenders are still stuck in the “allow all” mind-set to trust everything except code which does not pass certain tests or follows certain behavior. To exploit this mind-set an adversary only has to change their malware enough to bypass these filters (e.g. AntiVirus). As defenders update their blacklists/AntiVirus/firewalls, the malware authors make a small change or re-pack and re-deploy the malware bypassing the new rules/filters/etc.

For an adversary, changing their capability slightly and re-deploying is a relatively inexpensive operation – particularly with pervasive exploit kits such as BlackHole. Whereas the cost for the defender to find the new malware, develop a signature, and deploy that signature is relatively costly leaving the security accounting on the side of the adversary.

To win this battle, the defender must switch to a known-good model, or “deny all with exceptions.” Also known as the white list. However, as we have seen – this simply adds a new target for the adversary: the white list itself.