Cybercrooks behind the Sundown Exploit Kit are rapidly updating the hacking tool in a bid to exploit a gap in the market created by the demise of the Angler and Nuclear exploit kits.

While RIG and Neutrino have been the primary protagonists in the void left by Angler and Nuclear, Sundown is also vying for an increased share in the exploit kit marketplace.

Security researchers at Zscaler ThreatLabZ reckon the miscreants behind Sundown have accelerated the evolution of what started out as a fairly rudimentary exploit kit since the beginning of 2016.

The crooks behind Sundown used stolen code from the rival RIG exploit kit for a short time before subsequently knitting together their own code, security researchers at cloud security firm Zscaler ThreatLabZ report.

Elements of the latest version of the cybercrime toolkit include an image referencing the self-styled Yugoslavian Business Network – likely a reference to the infamous Russian Business Network cybercrime group.

Zscaler ThreatLabZ researchers commented: “This Russian Business Network inspired group may or may not be responsible for Sundown, but there does appear to be a German language group offering coding services on forums under the YBN moniker, with many commenters voicing their pleasure with the services.”

Since the disappearance of the two top exploit kits, Angler and Nuclear, other kits will be fighting for market share,” Zscaler ThreatLabZ concludes. “Sundown remains technically less sophisticated than others, but … Sundown's authors will surely keep making rapid updates to their code.”

Exploit kits in general are used to booby-trap websites in order to sling malware at visiting surfers through drive-by-download attacks. The tactic relies on exploiting security holes in typically Windows PCs, browser vulnerabilities and (increasingly) Flash flaws. ®