Exploring the hidden facets of malicious software and detection strategies
In a recent report titled Hidden Malware Report 2025 by Stairwell, the analysis of 769 threat reports published between March 2023 and July 2025 revealed a concerning trend. The report highlighted the prevalence of malware variants that have managed to slip past traditional security tools due to their reliance on exact matches.
Mike Wiacek, CTO of Stairwell, emphasized the importance of this finding, stating, "If you're relying on static hashes, you're fighting yesterday's threats."
The report found that older malware families tend to have more variants due to continuous reuse and small adjustments by attackers. Attackers often take what works and make small changes, like repacking a file, tweaking code, or renaming parts of it to generate new malware variants.
These slight modifications can create blind spots that attackers can exploit for extended periods. In fact, the analysis of certain files uncovered over 16,000 additional malware variants that were not included in the original reports.
Each threat report in the study contained more than 10,000 malware file identifiers, with an average of 13 hashes of known malware samples included. However, the search results did not contain any information about malware variants discovered in the 2025 Stairwell report or their development since 2023.
The average number of hashes shared in threat reports increased from 11 in 2023 to 18 in 2025, suggesting a growing awareness and effort to share threat intelligence.
To improve defenses against such malware variants, security teams are advised to adopt a continuous analysis strategy. This involves regularly reanalyzing files with new threat intelligence, continuously hunting for threats, updating rules, and searching for signs of compromise.
A "Back to basics" webinar on the CIS Security best practices ecosystem is suggested as a resource for teams seeking guidance on how to implement these strategies effectively.
The biggest danger of hidden threats is false confidence, leading to delayed response times and missed opportunities to stop an attack. As such, it is crucial for organisations to stay vigilant and proactive in their approach to cybersecurity.
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