Irok.Trojan.Worm

Irok.Trojan.Worm is a malicious worm that spreads itself using Microsoft Outlook email and Internet Relay Chat (IRC). The worm is sent as an email attachment. The message contains the following text:

Subject:

I thought you might like to see this.

Email message:

I thought you might like this.I got it from paramount pictures website.It's a startrek screen saver.

Type:	Trojan Horse, Virus, Worm
Infection Length:	10001 Bytes

Virus Definitions (Intelligent Updater) March 27, 2000

Wild Number of infections: 0 - 49 Number of sites: 0 - 2 Geographical distribution: Low Threat containment: Easy Removal: Easy

Threat Metrics Wild: Low Damage: High Distribution: Medium

Damage

• Payload Trigger: Email attachment Irok.exe is executed.
• Payload: Modifies executable files and corrupts them
  • Large scale e-mailing: List of up to 60 locations, using MS Outlook.
  • Degrades performance: Corrupts executable files such as Norton AntiVirus scanners to function improperly.
  • Causes system instability: System might not be able to restart.

Distribution

• Subject of email: I thought you might like this.
• Name of attachment: Irok.exe
• Size of attachment: 10001 Byte
• Shared drives: Shared network drives and partitioned drives.
• Target of infection: .Exe and .com files.

When Irok.exe is run, a black screen appears. Press Esc or the Spacebar to quit the application. It prepends itself to executable files and has been known to corrupt its host.

In the background, the worm copies itself to C:\Windows\System directory and inserts the Irokrun.vbs file into C:\Windows\StartMenu\Startup. The Irokrun.VBS script uses Microsoft Outlook to send the same email to the first 60 entries in the user's address book.

The third file to be dropped into an infected computer is called Winrde.dll in C:\Windows\System. From this point on, all executable files are infected and won't run properly.

When users restart, the Irokrun.vbs file is executed on computers with a Windows Sripting Host installed. Windows 98 users are vulnerable to this while Windows 95 users would need the Scripting Host installed. The Irokrun.vbs script uses Microsoft Outlook to send the same email to the first 60 entries in the user's address book. It attaches Irok.exe from C:\Windows\System directory.

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.

The infectious files Irok.exe, Irokrun.vbs, and Winrde.dll should be deleted. Users should also delete all files detected as Irok.Trojan.Worm(G1) and Irok.Trojan.Worm(G2). Irok has been reported to infect systems so that they will not restart. In this case, users need to restore the system from backup.

Write-up by: Edric Ta