StealC Malware Gets Stealthier With New Data Theft Upgrades

Cybercriminals behind StealC, a popular information-stealing malware, released a major update in March 2025, introducing new stealth capabilities and data theft tools. The update, detailed in a new report by Zscaler researchers, enhances the malware’s ability to avoid detection and steal sensitive data.

Now at version 2.2.4, StealC includes several upgrades that make it harder to detect and more effective at data exfiltration. First discovered in early 2023, the malware quickly gained traction on the dark web, selling for $200 per month. Since then, it has been used in large-scale attacks and malvertising campaigns throughout 2024. One notable upgrade allowed it to bypass Chrome’s App-Bound Encryption by regenerating expired cookies to hijack Google accounts.

Zscaler’s analysis highlights several new capabilities. The malware can now deliver malicious payloads via executable files, MSI installers, and PowerShell scripts. Attackers can customize when these payloads execute, giving them more control over attack timing. Communication with command-and-control servers is now encrypted using RC4, with randomized response parameters to evade detection tools.

StealC's architecture has also been overhauled. The malware now supports payloads for 64-bit systems and uses dynamic API resolution during runtime. A new self-destruct mechanism helps eliminate forensic traces post-execution. Additionally, a built-in builder lets cybercriminals generate custom variants, tailoring data theft parameters for specific individuals or organizations.

Another significant addition is the integration of a Telegram bot, which alerts operators in real time when new data is captured. The malware can now also take screenshots — supporting multi-display setups — significantly boosting its surveillance capabilities.

Interestingly, the latest version removes certain features, including virtual machine checks and DLL download/execution capabilities. Researchers suggest the change may reflect a codebase overhaul or a strategic shift toward a leaner toolset.

Zscaler also found that StealC has been deployed by Amadey, another malware loader, though the delivery methods vary across campaigns. We previously reported on StealC’s role in compromising over 6,000 WordPress sites in a widespread infostealer campaign, underscoring its versatility and reach.

To mitigate risks, experts advise users to enable multi-factor authentication, avoid downloading files from untrusted sources, and refrain from storing sensitive data in browsers.