A wave of attacks that have recently affected banks and other enterprises used open-source penetration testing tools loaded directly into memory instead of traditional malware, making their detection much harder.Researchers from antivirus vendor Kaspersky Lab started investigating these attacks after the security team from an unnamed bank found Meterpreter in the random access memory (RAM) of a server that acted as the organization's Windows domain controller.Meterpreter is an in-memory attack payload that can inject itself into other running processes and is used to establish persistency on a compromised system. It is part of the Metasploit penetration testing framework, a popular tool used both by internal security teams and by malicious hackers.During their analysis, the Kaspersky researchers found obfuscated PowerShell scripts stored in the system registry of the affected server that were designed to load Meterpreter directly into RAM, without leaving any traces on the hard disk drive.Those scripts had been generated with the Metasploit framework and had been configured to be executed by a malicious service that was manually set up with the SC Windows command-line utility.PowerShell is a scripting language and interpreter built into Windows that allows the automation of system administration tasks.Attackers also used the Windows NETSH utility to set up proxy tunnels through other internal computers in order to remotely control the system where Meterpreter was running without raising suspicion by directly opening connections to external IP addresses.The use of Windows utilities like SC, NETSH and PowerShell require administrator privileges, which attackers obtained by stealing credentials with Mimikatz, another tool that's popular with penetration testers.These fileless attack techniques are becoming more common, especially against organizations from the banking sector, the Kaspersky researchers said in a blog post. "Unfortunately the use of common tools combined with different tricks makes detection very hard. In fact, detection of this attack would be possible in RAM, network and registry only."Using its sensor network, Kaspersky found similar PowerShell scripts inside the registry of computers from around 100 other enterprise networks worldwide. The U.S., France, Ecuador, Kenya and the U.K. are the countries with the largest number of affected networks.In addition to making detection very hard, the use of standard Windows utilities and open source tools instead of traditional malware programs makes attribution very hard. It's not clear if these attacks are being perpetrated by a single group of hackers or by several ones.Over the past several years attackers have started to move away from targeting bank customers and going directly after the banks themselves. There are multiple gangs that specialize in hacking into banks' networks and then study their internal procedures in preparation for large-scale money heists. Others try to gain access to the ATM networks in order to force such machines to dispense money on command.