Hackers have developed a sophisticated StealRat botnet, capable of bypassing firms’ advanced anti-spam defences, according to security firm Trend Micro. Trend Micro threat response engineer, Jessa De La Torre reported uncovering the botnet, claiming that it uses advanced techniques to hide the malware used in the scam. “While exploiting vulnerable websites to send out spam has already been exhausted by other botnets, StealRat stood out because it used simple yet subtle methods to improve the botnet’s resiliency,” wrote De La Torre. De La Torre said by removing the interaction between the spam message and the campaign’s central server, the criminals are able to bypass most businesses’ cyber defences.