“Now, fileless malware is going mainstream, as financially motivated criminal hackers mimic their nation-sponsored counterparts. According to research Kaspersky Lab plans to publish Wednesday, networks belonging to at least 140 banks and other enterprises have been infected by malware that relies on the same in-memory design to remain nearly invisible. Because infections are so hard to spot, the actual number is likely much higher. Another trait that makes the infections hard to detect is the use of legitimate and widely used system administrative and security tools—including PowerShell, Metasploit, and Mimikatz—to inject the malware into computer memory.”
Source: A rash of invisible, fileless malware is infecting banks around the globe | Ars Technica