Trojan.Dasmin.B

SUMMARY

Trojan.Dasmin.B is a Trojan horse and a variant of Trojan.Dasmin. This Trojan horse tries to disguise the files it creates as Windows System files.

Trojan.Dasmin.B also sends users to specific Web pages, so that a counter on a page is incremented with each page hit. The author of this Trojan horse probably set up the Web page.

This threat is compressed with UPX.

Protection

• Virus Definitions (LiveUpdate™ Weekly) February 5, 2003
• Virus Definitions (Intelligent Updater) January 30, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

When Trojan.Dasmin.B runs, it does the following:
1. Creates two copies of itself as:

• C:\%System%Scvhost.exe
• C:\%System%Regcpm32.exe
  
  NOTE: %System% is a variable. The Trojan locates the System folder and copies itself to that particular location. By default, the location is at C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
  
  These files have random date stamps and have their file attributes set to Hidden and Archive.

2. Adds these values:

MSStartOptimizer C:\%System%Scvhost.exe
RegCompres C:\%System%Regcpm32.exe

to both of these registry keys:

HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
HKEY_LOCAL_MACHINESoftwareMicrosoftWindows
CurrentVersionRunServices

NOTE: Trojan.Dasmin.B recreates the registry values and dropped files every five seconds to ensure that they exist, even if you attempt to remove them or change the file attributes.

3. Attempts to access a specific Web site that contains a statistical counter. Most likely, the writer of Trojan.Dasmin wants to know how many systems have been infected with Trojan.Dasmin.B.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
• Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
• Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.

REMOVAL

These instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

1. Update the virus definitions.
2. Restart in Safe mode.
3. Run a full system scan and delete all the files detected as Trojan.Dasmin.B.
4. Restart in Normal mode and delete the values that the Trojan Horse added to the registry.
   

For specific details on each of these procedures, read the following instructions.

1. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:

• Running LiveUpdate, which is the easiest way to obtain the virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate), in the "Protection" section, at the top of this writeup.
• Downloading the definitions using the Intelligent Updater. The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater), in the "Protection" section, at the top of this writeup.
  
  The Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

2. Restarting the computer in Safe mode
All the Windows 32-bit operating systems, except Windows NT, can be restarted in Safe mode. For instructions on how to do this, read the document, "How to start the computer in Safe Mode."


3. Scanning for and deleting the infected files

1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan All Files."
2. Run a full system scan.
3. If any files are detected as infected with Trojan.Dasmin.B, click Delete.

4. Deleting the value from the registry

CAUTION: Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry," for instructions.

1. Restart the computer in Normal mode.
2. Click Start, and then click Run. (The Run dialog box appears.)
3. Type regedit, and then click OK. (The Registry Editor opens.)
4. Navigate to the keys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindows
   CurrentVersionRunServices
   
   NOTE: Both keys may not exist on all the operating systems.
   
5. In the right pane, delete the values:
   
   MSStartOptimizer C:\%System%Scvhost.exe
   RegCompres C:\%System%Regcpm32.exe
   
6. Exit the Registry Editor.