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F-Secure Virus Descriptions : IRC backdoor

[Summary] | [Disinfection]



NAME:IRC backdoor
ALIAS:Backdoor.IRC, Backdoor, IRC

Summary

IRC Backdoor (generic description)

An IRC backdoor is usually a standalone file that copies its file to Windows or Windows System folder and creates a Registry key to start that file during every Windows session. Also some IRC backdoors modify WIN.INI and SYSTEM.INI files or copy themselves to startup folders for different users. Some IRC backdoors replace INI scripts of an IRC client (mostly mIRC).

When an IRC backdoor is run, it established connection to an IRC server or waits until a user connects to IRC (mIRC script-based backdoor). A backdoor then creates a bot in a specific channel on a specific IRC server. An IRC bot acts as a backdoor server interface. An IRC client in this case acts as a backdoor client. A hacker can give commands to an IRC bot using IRC interface.

Most of advanced IRC backdoors allow to get a limited access to an infected system and to modify, upload, download and run files. Some IRC backdoors have additional functionalities that allow a hacker to perform malicious actions in IRC channels and in some cases can allow an attacker to completely take over an IRC channel.

Most famous IRC backdoors: SDBot, Roron, Nymph.

Disinfection

Automatic Disinfection

Usually standalone malware (backdoors, worms, trojans, etc.) is automatically removed by F-Secure Anti-Virus (FSAV) starting from version 5.40. Malware files get automatically renamed by FSAV, so they can not be started any more. In some rare cases, when automatic disinfection is not possible, a user can select disinfection action by him/herself to make FSAV rename or delete an infected file. In some special cases it is recommended to use specific disinfection tools provided by F-Secure. They can be downloaded from our ftp site:

ftp://ftp.f-secure.com/anti-virus/tools/

F-Secure Anti-Virus can be purchased from our webshop or from our authorised distributors. A trial version F-Secure Anti-Virus, limited to 30 days, can be downloaded from our website:

http://www.f-secure.com/download-purchase/

All the latest versions of FSAV can download anti-virus database updates automatically. However, these updates can be also downloaded and installed manually from our web or ftp sites:

http://www.f-secure.com/download-purchase/updates.shtml

Manual Disinfection

To manually disinfect standalone malware (backdoors, worms, trojans, etc.) it's usually enough to delete all infected files from a computer and to restart it. Active malware files are usually locked by operating system so different disinfection approaches are required for different operating systems.

Please note that manual disinfection is a risky process, so it is recommended only for advanced users.

Windows 95, 98, ME

If Windows 9x operating system is used, it is recommended to restart a computer from a bootable system diskette and to delete an infected file from command prompt. For example if a malicious file named ABC.EXE is located in Windows folder, it is usually enough to type the following command at command prompt:

DEL C:\WINDOWS\ABC.EXE

and to press Enter. After that an infected file will be gone.

Windows NT, 2000, XP

If Windows NT, 2000 or XP is used, a malicious file has to be renamed with a different extension (for example .VIR) and then a system has to be restarted. After restart a renamed malicious file will no longer be active and it can be easily deleted manually.

System Restore issue

If Windows ME or XP is used, it is recommended to disable System Restore feature of these operating systems to prevent a computer from re-infection by an already removed malware. The fact is that System Restore feature of these operating systems might save an infected file into the special folder and copy it back to a hard drive it every time it's been renamed or deleted by F-Secure Anti-Virus or by a user. Instructions on how to disable System Restore feature are here:

Windows ME: http://www.europe.f-secure.com/v-descs/sfc_dis.shtml

Windows XP: http://www.europe.f-secure.com/v-descs/sfc_dis1.shtml

It is recommended to re-enable System Restore after disinfection in order to restore stable system configuration in the future, if any crash or incompatibility issue occurs.

Contacting F-Secure for help

If you have problems with disinfection, please consult a computer technician or send a message (and a sample) to our Viruslab. We have guidelines for sending virus samples, hoaxes and virus-related questions to F-Secure Viruslab published here:

http://support.f-secure.com/enu/home/virusproblem/sample/

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Writeup: Alexey Podrezov, July 14th, 2003;

Description Updated: Alexey Podrezov, May 24th, 2004;

F-Secure Corporation