Mac.c Stealer Takes on AMOS:A New Rival Shakes Up the macOS Infostealer Market | HackerNoon
hackernoon.com - Moonlock analysed Mac.c stealer, a new rival to AMOS. Learn its tactics, code reuse, and "building in public" strategy. The story of the Mac.c stealer doesn’t begin with a major campaign or breach. It starts in the hushed corners of darknet forums, where a threat actor named 'mentalpositive' first emerged, drawing attention with a set of unusual traits that set him apart from other stealer developers. Moonlock, the cybersecurity division of MacPaw, has been tracking mentalpositive for the past four months. We can already see that it is a new actor taking advantage of a macOS malware market that remains far less saturated than its Windows counterpart, marking the rise of the new wave of threat actors who are both technically skilled and commercially ambitious. Although only recently active, Mac.c is already competing with larger, more established stealer operations like Atomic macOS Stealer. While it borrows heavily from AMOS and Rodrigo4 malware, it's tailored for quicker, high-impact data theft. As more URLs are added to its command-and-control infrastructure, Mac.c appears to be part of a larger underground ecosystem targeting macOS users. What also stands out is a methodical and unusually transparent approach to building in public. 'mentalpositive' shared progress updates and even collected feedback on Mac.c builds — a surprising level of openness in the typically secretive world of macOS malware development. In this article, we trace the evolution of Mac.c, unpack mentalpositive’s tactics, and examine how this stealer fits into the broader landscape of threats targeting Apple platforms. A new player on the market About four months ago, Moonlock Lab first noticed the emergence of the Mac.c stealer and attributed it to a developer under the alias 'mentalpositive'. This threat actor was one of many new players entering the macOS malware market, a space still far less crowded than the Windows-targeting malware industry. Similar to other threat actors, 'mentalpositive' adopts recent trends in malware development: modular architecture for use across different campaigns, advanced obfuscation techniques, and increasingly complex command-and-control (C2) infrastructures. However, the target profile and data exfiltration scope of mentalpositive’s Mac.c stand out. It harvests iCloud Keychain credentials, browser-stored passwords, crypto wallets, system metadata, and even files from specific locations on macOS — all using credentials obtained through phishing. By relying on standard system APIs and staged communication methods, it evades many traditional endpoint defences. Building in public Beyond technical design, 'mentalpositive' exhibited unusual behavior across darknet forums. Over the span of several months, this threat actor used one underground forum to showcase incremental updates to Mac.c, engage with potential users, and actively solicit feedback. Such publicity may signal an intent to raise visibility and carve out a distinct market presence. It also appears to lay the groundwork for a custom stealer-as-a-service business model aimed squarely at the macOS threat niche. The screenshots below show how the forum posts evolved over time as new features were announced. Since the original posts were written in Russian, we’ve included a brief explanation for each. The first screenshot shows an early advertisement offering a subscription to stealer updates for $1,500 per month.
