How to Detect and Remove F-Opasrv Malware From Infected Networks
F-Opasrv (commonly documented as Opaserv or Opasoft) is a highly aggressive network worm that spreads efficiently across local area networks (LANs) and wide area networks (WANs). It specifically exploits system vulnerabilities like Microsoft Windows NetBIOS services and unsecure Share Level Passwords to compromise remote hosts automatically. Once inside, it installs a backdoor routine, drops malicious payload executables, and modifies system configuration parameters to maintain persistence.
Securing an enterprise or home network from this threat requires a multi-phased incident response playbook encompassing immediate containment, detection, eradication, and systemic hardening. 1. Network Containment and Isolation
The primary strength of the F-Opasrv worm is its rapid propagation capability. Immediate containment is vital to stop the lateral movement of the payload.
Isolate Compromised Systems: Physically disconnect any suspected machine from the local network by removing the Ethernet cable or disconnecting from the Wi-Fi.
Block Port Traffic: Temporarily drop inbound and outbound traffic on Port 137, 138, 139, and 445 (NetBIOS and SMB services) at the internal firewall or switch level. This stops the worm from scanning and copying itself to adjacent network shares.
Disable Unsecure Network Shares: Temporarily disable unauthenticated network drives, open administrative shares, and public folders across the network directory. 2. Detection and Identification Mechanisms
F-Opasrv drops specific indicators of compromise (IOCs) on host machines. Network administrators can hunt for these artifacts manually or via centralized logging tools. Registry Persistence Keys
The worm ensures it runs on system boot by editing auto-run keys. Inspect host registries for the following modification: Path: HKLM\Software\Microsoft\Windows\CurrentVersion\Run Value: ScrSvr = %malware_filename%.exe Malicious File Drop Signatures
F-Opasrv and its subsequent variants mask themselves under specific file names inside the local Windows directory. Scan for the presence of these exact 28KB Portable Executable (PE) files: scrsvr.exe (Standard Opaserv payload) alevir.exe (Opaserv.F variant) puta!!.exe (Opaserv.G variant) mqbkup.exe (Opaserv.L variant) Network Logs
Review internal network firewall and Intrusion Detection System (IDS) alerts. Look for repetitive, automated probing requests targeted toward Port 137 or Port 139 originating from a single internal IP address. 3. Removal and Eradication Step-by-Step
Because F-Opasrv blocks or subverts normal processes, removal must be performed meticulously while the host is detached from the network.
[Isolate Device] ➔ [Boot into Safe Mode] ➔ [Terminate Active Processes] ➔ [Purge Registry & Files] ➔ [Full AV Scan] Step 1: Boot into Safe Mode
Restart the infected host and enter Safe Mode with Command Prompt. This prevents the malware from executing its auto-run routine during initialization, locking down the file for deletion. How to remove a computer virus or malware – Kaspersky
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