Trojan:Win32/AgentBypass is a detection for files that attempt to inject possibly malicious code into the "explorer.exe" process.
"Explorer.exe" is the Windows default shell and is usually exempt from or in the trusted list of a software-based firewall rule allowing inbound and outbound network traffic.
The function of the injected code may vary but most samples are designed to load a DLL file into the "explorer.exe" process that bypasses the firewall. The code may also serve as a rootkit that interferes with the normal operation of "explorer.exe", such as hide files and folders from the user. It could also allow the trojan to steal data and login details from the affected computer and send these to a remote server.
Analysis by Marianne Mallen
Alert notifications or detections of this malware from installed antivirus or security software may be the only other symptoms.