This attack could pose a serious security threat. You should take immediate action to stop any damage or prevent further damage from happening.
This signature detects attempts to exploit a vulnerability in Powershell which could result in remote code execution.
PowerShell is a Windows task automation framework. It consists of a command-line shell and a scripting language based on the .NET framework.
When an attacker has physical access to the target machine, a simple Powershell command can load a waiting payload in a remote server via HTTP. This payload is loaded in memory and does not write to the disk so it potentially evade AV detections.