BW.770.B

SUMMARY

BW.770.B is a virus that infects DOS .exe and .com files. It is 770 bytes in size, and it appears to have been created with the "Biological Warfare" virus creation kit . The virus appears to have been modified manually after being created with the kit. BW.770.B can be inserted on your system by the "futs" hackers tool.

NOTE: This virus was previously detected as Bloodhound.Filestring. All viruses that can be created with the Biological Warfare virus creation kit will be detected by Norton AntiVirus.

Behavior

Symptoms

Transmission

Protection

• Virus Definitions (Intelligent Updater) April 6, 2001

TECHNICAL DETAILS

BW.770.B does not go memory resident. Instead, it does a recursive search on the system and infects any DOS .exe or .com files that it finds. The virus will also infect Portable Executable (PE) files. However, when running an infected PE file, the virus will not execute.

When infecting .com files, the virus overwrites the first 3 bytes with a jump to end-of-file (EOF). It then appends itself to the EOF. As a result, the jump at the beginning of the .com file is pointing to the start of the viral body, and the virus receives immediate control when an infected .com file is executed. After the virus has finished its malicious activities on the system, it restores the 3 bytes that it overwrote, and then executes the original host.

The infection for executable files is carried out slightly differently than the infection of .com files. First the virus determines if a file is a DOS executable file. This is done by checking for the letters MZ at the start of the file. It is possible, even though it is not common, for DOS executable files to have ZM instead of MZ as the first two bytes of the file. In this case, BW.770.B will not infect the file. Once the virus has determined that the file is an MZ executable, it will append itself at the end and change the entry point to point to itself. The virus will store the original entry point within itself, and once it is done executing, it will jump to the original entry point. An executable file infected with this virus will be detected as BW.770.B (x).

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

To remove this virus:

1. Run LiveUpdate to make sure that you have the most recent virus definitions.
2. Start Norton AntiVirus (NAV), and then run a full system scan, making sure that NAV is set to scan all files.
3. If any files are detected as infected by BW.770.B, choose Repair.