Businesses increasingly use whitelisting to keep the bad guys out but now it turns out that criminals are employing the same tactics to target favoured victims, security firm RSA has reported.
During 2012, the company saw a small surge in the popularity of plug-in modules for phishing kits that allow their users to aim attacks at specific targets in a way that excludes unintended victims.
Dubbed the "bouncer" attack (as in club bouncers), these generate user IDs for each target on the list, serving unwanted visitors a 404 for the same phishing site.
A huge surprise is the tiny scale of some of these attacks; 3,000 recipients was an average for campaigns.
Selective phishing isn't new per se but its emergence as a more regular tactic is partly a response to the predation of security firms, who make a living from detecting, analysing and blocking attacks in real time. Keeping these researchers out buys the attackers more time.
A second motivation is simply spear phishing, campaigns that target specific enterprises with a view to setting up more complex advanced persistent threat (APTs) attacks at a later date.
"The peculiar approach is likely the work of a gang or a fraud service vendor supplying credentials to specific geographical regions and targets," said RSA cybercrime specialist, Limor S Kessem.
As with most phishing websites these days, the pages on which these attacks hide will usually be hijacked blogs using vulnerable and poorly-managed open source content management systems. Hiding on legitimate domains is a way of hiding in plain sight.
"With phishing attacks popping up like mushrooms and then quickly taken down, arriving at a 404 page for a reported phish could present a detection challenge for the industry," predicted Kessem.
Despite being one of the most established attacks, 2012 was a record year for phishing, RSA said, with recorded attacks up 59 percent over the previous year.
Global fraud damages from phishing rose to $1.5 billion (£950 million), up 22 percent on 2011.