Stealien (스틸리언) is a South Korean cybersecurity company founded in 2015, headquartered in Seoul (Yongsan-gu), with additional offices in Japan (Tokyo) and Indonesia (Jakarta). The company's name is derived from the phrase "we STEAL ALIEN technology," reflecting a self-described ethos of working at the cutting edge of security research. The company's primary product line is the AppSuit Series, a suite of mobile application security solutions. AppSuit encompasses multiple modules, including AppSuit Remote Block, AppSuit Anti-Capture, AppSuit WBC (White-Box Cryptography), AppSuit AV (Anti-Virus), and AppSuit Keypad — all of which have received GS (Good Software) Grade 1 certification from Korean authorities. These products are designed to protect mobile applications against reverse engineering, tampering, screen capture, and other threats. In addition to mobile app security products, Stealien operates a Cyber Drill System — a platform for cybersecurity training, hacking education, and competition management. The company also provides security consulting services, including penetration testing conducted from an attacker's perspective, as well as cybersecurity R&D conducted in collaboration with government agencies and research institutions. Stealien holds ISO 27001:2022 and ISO 27001:2013 certifications, and has been recognized multiple times by South Korean government bodies including the Ministry of Science and ICT and the National Intelligence Service. The company has been named an Asia-Pacific high-growth company by the Financial Times three consecutive years (2022–2024). It holds multiple Korean, Japanese, and Indonesian patents related to its security technologies.