XP

The Russian gang behind the obscure Qbot botnet have quietly built an impressive empire of 500,000 infected PCs by exploiting unpatched flaws in mainly US-based Windows XP and Windows 7 computers, researchers at security firm Proofpoint have discovered.

A year or two ago, what the Qbot (aka Qakbot) campaign has achieved in the roughly half dozen years the actors behind it have been operating would have been seen as a major concern. Recently, standards have gone up a notch.