Malware type: Worm

Aliases: Net-Worm.Win32.Opasoft.a (Kaspersky), W32.Opaserv.Worm (Symantec), Worm/OpaSoft.AA (Avira), W32/Opaserv-A (Sophos),

In the wild: Yes

Destructive: No

Language: English

Platform: Windows 95, 98, ME

Encrypted: No

Overall risk rating:

Reported infections:

Damage potential:


Distribution potential:


Infection Channel 1 : Propagates via network shares

Infection Channel 2 : Propagates via software vulnerabilities


This worm takes advantage of the Share Level Password vulnerability on Windows systems to propagate via network shared C:\ drives. This vulnerability allows a remote user to access a Windows 9x/ME shared file without having to know the entire password assigned to that share. More information on this vulnerability is available at:

This worm attempts to download what appears to be updated copies of itself from a certain site. At this time of writing, the download site is not accessible and is either blocked or currently down.

It drops and executes the file flcss.exe, which is detected by Trend Micro as PE_Funlove.4099, in the Windows system folder.

Moreover, it scans for the computer name and domain name of machines connected to the network, and then sends this information to the download site.

For additional information about this threat, see:

Description created: Sep. 30, 2002 3:26:44 AM GMT -0800


File type: PE

Memory resident:  Yes

Size of malware: 28,672 Bytes

Initial samples received on: Sep 2, 2002

Vulnerability used:  (MS00-072) Share Level Password Vulnerability

Related toPE_FUNLOVE.4099

Payload 1: Downloads files

Payload 2: Drops files

Payload 3: Steals information

Installation and Autostart

Upon execution, this worm drops a copy of itself in local machine and all remote machines with shared drives as:

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

It deletes the copy that was originally executed, provided that the copy is not located in the Windows folder.

It also drops and executes the file flcss.exe, which is detected by Trend Micro as PE_Funlove.4099, in the Windows system folder.

This worm creates the following registry entry so that it automatically executes at every Windows startup:

ScrSvr = "%Windows%\SCRSVR.EXE"

At the same time, on remote machines, this worm creates the file TMP.INI in drive C and copies the contents of WIN.INI into this file. It then adds the following strings in the [windows] section of TMP.INI.

run = "C:\%Windows%\SCRSVR.EXE"

Propagation via Network Shares and Software Vulnerability

This worm propagates via network shared C:\ drives using the Share Level Password vulnerability. This vulnerability allows a remote user to access a Windows 9x/ME shared file without having to know the entire password assigned to that share. If the drive is protected with a password, the worm uses a brute force technique to gain access to the shared drive.

To scan the network, it uses the standard Netbios nbstat frames, which elicits a node status response from Netbios and SAMBA clients. The response contains a listing of any Netbios name known to that node.

The infection process begins with a nbstat request frame. When the nbstat is answered, this worm follows it with a TCP session at port 139, which attempts to mount to a share named C.

If successful, this worm loads itself in the Windows folder as a file named scrsvr.exe. It looks for machines in the same domain that has shared C:\ drives with full access.

This worm registers itself as a service and repetitively scans for machines connected to the network. It uses Server Message Block Protocol (SMB) commands to access the shared drives.

More information on the Share Level Password vulnerability is available at:

Other Details

It appears that this worm sends information to the site, http://www.{BLOCKED}asoft.com. Also apparent in its codes is that it downloads updated copies of itself from the Web site. However, at the time of this writing, the site is down and inaccessible.

This worm also drops the files, SCRSIN.DAT and SCRSOUT.DAT in drive C:


It uses these files during the information exchange with http://www.{BLOCKED}asoft.com.

This worm also creates the following mutex to ensure that only one instance of this worm is running in the memory:


Affected Platforms

This worm runs on Windows 95, 98, and ME

Analysis By: Xavier Capilitan

Updated By: Ricardo O. Pineda Jr.

Revision History:

First pattern file version: 705
First pattern file release date: Sep 02, 2002
Mar 23, 2006 - Modified Virus Report


Minimum scan engine version needed: 7.500

Pattern file needed: 3.211.00

Pattern release date: Feb 14, 2006

Important note: The "Minimum scan engine" refers to the earliest Trend Micro scan engine version guaranteed to detect this threat. However, Trend Micro strongly recommends that you update to the latest version in order to get comprehensive protection. Download the latest scan engine here.

NOTE: Before proceding to remove this malware, Trend Micro recommends that infected machines be temporarily disconnected from the network.


To automatically remove this malware from your system, please refer to the Trend Micro Damage Cleanup Services.


Note: To fully remove all associated malware, perform the clean solution for PE_FUNLOVE.4099.

Terminating the Malware Program

This procedure terminates the running malware process.

  1. Open Windows Task Manager.
    On Windows 95, 98, and ME, press
  2. In the list of running programs*, locate the process:
  3. Select the malware process, then press either the End Task or the End Process button, depending on the version of Windows on your computer.
  4. To check if the malware process has been terminated, close Task Manager, and then open it again.
  5. Close Task Manager.

*NOTE: On computers running Windows 95, 98, and ME, Windows Task Manager may not show certain processes. You can use a third party process viewer such as Process Explorer to terminate the malware process.

On computers running all Windows platforms, if the process you are looking for is not in the list displayed by Task Manager or Process Explorer, continue with the next solution procedure, noting additional instructions. If the malware process is in the list displayed by either Task Manager or Process Explorer, but you are unable to terminate it, restart your computer in safe mode.

Editing the Registry

This malware modifies the computer's registry. Users affected by this malware may need to modify or delete specific registry keys or entries. For detailed information regarding registry editing, please refer to the following articles from Microsoft:

  1. HOW TO: Backup, Edit, and Restore the Registry in Windows 95, Windows 98, and Windows ME

Removing Autostart Entry from the Registry

Removing autostart entries from the registry prevents the malware from executing at startup.

If the registry entry below is not found, the malware may not have executed as of detection. If so, proceed to the succeeding solution set.

  1. Open Registry Editor. Click Start>Run, type REGEDIT, then press Enter.
  2. In the left panel, double-click the following:
  3. In the right panel, locate and delete the entry:
    ScrSvr = "%Windows%\SCRSVR.EXE"
    (Note: %Windows% is the default Windows folder, usually C:\Windows or C:\WINNT.)
  4. Close Registry Editor.

Deleting the Malware File

  1. Right-click Start then click Search... or Find..., depending on the version of Windows you are running.
  2. In the Named input box, type:
  3. In the Look In drop-down list, select the drive that contains Windows, then press Enter.
  4. Once located, select the file then press Delete.
  5. Repeat steps 2 to 4 to delete the following files:

Important Windows ME Cleaning Instructions

Users running Windows ME must disable System Restore to allow full scanning of infected computers.

Users running other Windows versions can proceed with the succeeding solution set(s).

Running Trend Micro Antivirus

If you are currently running in safe mode, please restart your computer normally before performing the following solution.

Scan your computer with Trend Micro antivirus and delete files detected as WORM_OPASERV.A. To do this, Trend Micro customers must download the latest virus pattern file and scan their computer. Other Internet users can use HouseCall, the Trend Micro online virus scanner.

Applying Patch

This malware exploits a known vulnerability in Windows. Download and install the fix patch supplied by Microsoft. Refrain from using this product until the appropriate patch has been installed. Trend Micro advises users to download critical patches upon release by vendors.

Trend Micro offers best-of-breed antivirus and content-security solutions for your corporate network, small and medium business, mobile device or home PC.