W32.Crypto

SUMMARY

W32.Crypto is not known to be in the wild yet. The payload for this virus is similar to the One_Half virus. This means the Crypto virus will encrypt the data on your hard drive, and if you remove the virus, the data will be inaccessible - and effectively held hostage. Crypto uses strong cryptographic algorithms to encrypt the data on the hard disk, making recovery unlikely without a backup.

W32.Crypto uses the Microsoft Crypto API to encrypt accessed DLLs on the system with an encryption key that is added by the virus to the infected system, and installed in the registry as:

SOFTWAREMicrosoftCryptographyUserKeysPrizzy/29A.

The virus first infects the operating system file KERNEL32.DLL. Once infected, KERNEL32.DLL controls all access to other DLLs on the system and the virus encrypts all such accessed DLL files. While the virus is active in memory, it will automatically decrypt encrypted DLL files so they can be used. However, if the virus is not active in memory, the DLLs will not be decrypted and the system will fail to work. Unless the virus is active and running, all DLL files that have been encrypted will be inaccessible. This means that an infected system can only be cleaned by restoring all affected DLL files from backup copies, and deleting all infected executable files. Data files are not encrypted by this release of the virus.

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

The virus infects PE (Windows Portable Executable) files by appending itself to the last section of the executable in encrypted form. The virus uses a complex polymorphic engine, meaning that the virus is self-mutating and difficult to detect. The size of the pure virus body is about 20 kilobytes, thus W32.Crypto is a very large virus.
During test infections, the virus failed to infect most systems and on others it infected a few files causing Windows to stop working. However in a few Windows installations, the virus does appear to work correctly.
When an infected file is executed, the virus infects KERNEL32.DLL in the Windows directory. It is interesting to note that the virus is not encrypted in the KERNEL32.DLL file, and its logic can be seen with any common viewing tools.
Infected KERNEL32.DLL files will contain a lot of visible strings including: Win32.Crypto, (c)oded by Prizzy/29A Greetz to Darkman, Benny and GriYo Kiss Of Death
In order to cause the infected KERNEL32 file to be used by the Windows operating system, the virus creates a wininit.ini file. This wininit.ini file instructs Windows to use the infected KERNEL32.DLL file the next time the machine is rebooted.
When the KERNEL32.DLL is infected, it will call the virus code as files are accessed on the system. The virus attempts to infect 20 files during boot time and also checks for known archive files and infects them by using the available archives on the machine such as: PKZIP.EXE, ARJ.EXE, RAR.EXE and ACE.EXE. The virus adds infected files to the archives it locates.
Crypto is a retro virus. It pays attention to certain software debuggers. It deletes anti-virus data files and also disables some active anti-virus protection.
The virus targets the following anti-virus files:

• AVP.CRC
• IVP.NTZ
• ANTI-VIR.DAT
• CHKLIST.MS,
• SMARTCHK.MS
• SMARTCHK.CPS
• AGUARD.DAT
• AVGQT.DAT
• LGUARD.VPS

W32.Crypto does not infect popular anti-virus software or some other common applications that have self-check routines. It will refrain from infecting programs with names beginning with:

• TB
• F-
• AW
• AV
• NAV
• PAV
• RAV
• NVC
• FPR
• DSS
• IBM
• INOC
• ANTI
• SCN
• VSAF
• VSWP
• PANDA
• DRWEB
• FSAV
• SPIDER
• ADINF
• SONIQUE
• SQSTART

The virus also avoids infecting specific system executable files that are monitored by the operating system for changes. Such protection is available in Windows 2000 and Windows 98SE.

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.