Stairwell is a cybersecurity company focused on malware analysis and threat detection, with a particular emphasis on identifying malware variants that evade traditional detection tools. The company's platform is described as "private by design, continuous by default," indicating an architecture built around ongoing, privacy-preserving file and threat analysis. Stairwell's core product centers on file analysis with AI-assisted triage, enabling security teams to analyze files for malicious characteristics. The platform surfaces hidden malware variants — threats that are related to known malware families but have been modified enough to bypass signature-based or hash-based detection methods. The company published research identifying over 16,000 hidden malware variants derived from analysis of 769 public threat reports, highlighting a gap in conventional detection approaches that rely on previously observed indicators. The platform integrates with a range of widely-used security tools including Palo Alto Cortex, Splunk, SentinelOne, Google Security Operations, CrowdStrike, Google Chronicle, Tines, Slack, and TheHive. It also positions itself as an alternative or complement to VirusTotal for file analysis. Stairwell's target market is enterprise security operations teams seeking to improve detection coverage beyond static indicators of compromise (IOCs). The company is backed by investors including Sequoia, Accel, Gradient Ventures, S32, and Allen & Company. It was co-founded by Mike Wiacek, who serves as CTO, and is led by CEO Emmy Linder.