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	"title": "W95.CIH | Symantec",
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	"plain_text": "W95.CIH | Symantec\r\nArchived: 2026-04-05 15:06:15 UTC\r\nThe Wayback Machine - https://web.archive.org/web/20190508170055/https://www.symantec.com/security-center/writeup/2000-122010-2655-99\r\nDiscovered: June 01, 1998\r\nUpdated: April 25, 2002 2:39:44 PM\r\nType: Virus\r\nSystems Affected: Windows\r\nW95.CIH, also commonly referred to as Chernobyl, is a destructive parasitic virus. It remains memory resident\r\nand infects other exe files when they are opened.\r\nDue to decreased submissions, Symantec Security Response has downgraded this threat level to 2 from 3 as of\r\nMarch 30, 2004.\r\nThe CIH virus, also known as Chernobyl, was first discovered in June 1998 in Taiwan. According to the Taipei\r\nauthorities, Chen Ing-hau wrote the CIH virus. The name of the virus derived from his initials.\r\nCIH is a destructive virus with a payload that destroys data. On April 26, 1999, the payload triggered for the first\r\ntime, causing many computer users to lose their data. In Korea, it was estimated that as many as one million\r\ncomputers were affected, resulting in more than $250 million in damages.\r\nAlthough the virus is rather old, Symantec still believes the virus is in the wild and may cause damage to\r\ncomputer users who use outdated virus definitions, or who do not use antivirus software.\r\nAntivirus Protection Dates\r\nInitial Rapid Release version June 28, 1998\r\nLatest Rapid Release version August 08, 2016 revision 023\r\nInitial Daily Certified version June 28, 1998\r\nLatest Daily Certified version August 09, 2016 revision 001\r\nInitial Weekly Certified release date June 28, 1998\r\nClick here for a more detailed description of Rapid Release and Daily Certified virus definitions.\r\nWriteup By: Motoaki Yamamura\r\nDiscovered: June 01, 1998\r\nUpdated: April 25, 2002 2:39:44 PM\r\nType: Virus\r\nSystems Affected: Windows\r\nhttps://web.archive.org/web/20190508170055/https://www.symantec.com/security-center/writeup/2000-122010-2655-99\r\nPage 1 of 5\n\nCIH is a virus that infects the 32-bit Windows 95/98/NT executable files, but can function only under Windows\r\n95/98 and ME. It does not function under Windows NT or Windows 2000. When an infected program is run under\r\nWindows 95/98/ME, the virus becomes resident in memory. To remove the virus, do one of the following:\r\nRecommended method: Use the Symantec Security Response CIH Removal Tool, which removes the virus\r\nfrom memory and prevents the need to reboot from a clean system disk.\r\nReboot the computer from a Rescue Disk.\r\nReboot the computer from the Norton AntiVirus (NAV) 2001/2002 CD, if your computer allows this\r\noption.\r\nIf this is not done, the virus will infect every file scanned with Norton AntiVirus or with any antivirus program.\r\nAlthough Windows NT system files can be infected, the virus cannot become resident or infect files on a computer\r\nrunning Windows NT or Windows 2000. The virus does not function under DOS, Windows 3.1, or on Macintosh\r\ncomputers. Once the virus is resident, the CIH virus infects other files when accessed.\r\nThe files infected by CIH may have the same size as the original files, due to the unique infection mode of CIH.\r\nThe virus searches for empty, unused spaces in the file. Next, it breaks itself up into smaller pieces and inserts its\r\ncode into these unused spaces. When NAV repairs a file infected by CIH, it looks for these small viral pieces and\r\nremoves them from the file.\r\nAs of April, 1999, three known, similar variants of this virus exist. CIH versions 1.2 and 1.3 have a payload that\r\nwill trigger on April 26, commemorating Chernobyl, the Soviet nuclear disaster, which occurred on April 26,\r\n1986. CIH version 1.4 has a payload that will trigger on the 26th of any month. The payloads of all the versions of\r\nCIH are the same.\r\nThe first payload overwrites the hard disk with random data, starting at the beginning of the disk (sector 0) using\r\nan infinite loop. The overwriting of the sectors does not stop until the system has crashed. As a result, the\r\ncomputer will not boot from the hard disk or floppy disk. Also, the data that has been overwritten on the hard disk\r\nwill be very difficult or impossible to recover. You must restore the data from backups.\r\nThe second payload tries to cause permanent damage to the computer. This payload attacks the Flash BIOS (a part\r\nof your computer that initializes and manages the relationships and data flow between the system devices,\r\nincluding the hard drive, serial and parallel ports, and the keyboard) and tries to corrupt the data stored there. As a\r\nresult, nothing may be displayed when you start the computer. A computer technician would need to fix this.\r\nRecommendations\r\nSymantec Security Response encourages all users and administrators to adhere to the following basic security\r\n\"best practices\":\r\nUse a firewall to block all incoming connections from the Internet to services that should not be publicly\r\navailable. By default, you should deny all incoming connections and only allow services you explicitly\r\nwant to offer to the outside world.\r\nEnforce a password policy. Complex passwords make it difficult to crack password files on compromised\r\ncomputers. This helps to prevent or limit damage when a computer is compromised.\r\nhttps://web.archive.org/web/20190508170055/https://www.symantec.com/security-center/writeup/2000-122010-2655-99\r\nPage 2 of 5\n\nEnsure that programs and users of the computer use the lowest level of privileges necessary to complete a\r\ntask. When prompted for a root or UAC password, ensure that the program asking for administration-level\r\naccess is a legitimate application.\r\nDisable AutoPlay to prevent the automatic launching of executable files on network and removable drives,\r\nand disconnect the drives when not required. If write access is not required, enable read-only mode if the\r\noption is available.\r\nTurn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit\r\naccess. Disable anonymous access to shared folders. Grant access only to user accounts with strong\r\npasswords to folders that must be shared.\r\nTurn off and remove unnecessary services. By default, many operating systems install auxiliary services\r\nthat are not critical. These services are avenues of attack. If they are removed, threats have less avenues of\r\nattack.\r\nIf a threat exploits one or more network services, disable, or block access to, those services until a patch is\r\napplied.\r\nAlways keep your patch levels up-to-date, especially on computers that host public services and are\r\naccessible through the firewall, such as HTTP, FTP, mail, and DNS services.\r\nConfigure your email server to block or remove email that contains file attachments that are commonly\r\nused to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.\r\nIsolate compromised computers quickly to prevent threats from spreading further. Perform a forensic\r\nanalysis and restore the computers using trusted media.\r\nTrain employees not to open attachments unless they are expecting them. Also, do not execute software\r\nthat is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised\r\nWeb site can cause infection if certain browser vulnerabilities are not patched.\r\nIf Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the\r\ndevice's visibility is set to \"Hidden\" so that it cannot be scanned by other Bluetooth devices. If device\r\npairing must be used, ensure that all devices are set to \"Unauthorized\", requiring authorization for each\r\nconnection request. Do not accept applications that are unsigned or sent from unknown sources.\r\nFor further information on the terms used in this document, please refer to the Security Response glossary.\r\nWriteup By: Motoaki Yamamura\r\nDiscovered: June 01, 1998\r\nUpdated: April 25, 2002 2:39:44 PM\r\nType: Virus\r\nSystems Affected: Windows\r\nRemoval using the CIH removal tool\r\nSymantec Security Response has developed a removal tool to clean the infections of W95.CIH. Use this removal\r\ntool first, as it is the easiest way to remove this threat.\r\nManual Removal:\r\nThe following instructions pertain to all current and recent Symantec antivirus products, including the Symantec\r\nAntiVirus and Norton AntiVirus product lines.\r\nhttps://web.archive.org/web/20190508170055/https://www.symantec.com/security-center/writeup/2000-122010-2655-99\r\nPage 3 of 5\n\n1. Disable System Restore (Windows Me/XP).\r\n2. Update the virus definitions.\r\n3. Run a full system scan.\r\nFor specific details on each of these steps, read the following instructions.\r\n1. To disable System Restore (Windows Me/XP)\r\nIf you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore.\r\nWindows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they\r\nbecome damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or\r\nTrojan on the computer.\r\nWindows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore,\r\nantivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has\r\nthe potential of restoring an infected file on your computer, even after you have cleaned the infected files from all\r\nthe other locations.\r\nAlso, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.\r\nFor instructions on how to turn off System Restore, read your Windows documentation, or one of the following\r\narticles:\r\nHow to disable or enable Windows Me System Restore\r\nHow to turn off or turn on Windows XP System Restore\r\nNote: When you are completely finished with the removal procedure and are satisfied that the threat has been\r\nremoved, reenable System Restore by following the instructions in the aforementioned documents.\r\nFor additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft\r\nKnowledge Base article: Antivirus Tools Cannot Clean Infected Files in the _Restore Folder (Article ID:\r\nQ263455).\r\n2. To update the virus definitions\r\nSymantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our\r\nservers. There are two ways to obtain the most recent virus definitions:\r\nRunning LiveUpdate, which is the easiest way to obtain virus definitions.\r\nIf you use Norton AntiVirus 2006, Symantec AntiVirus Corporate Edition 10.0, or newer products,\r\nLiveUpdate definitions are updated daily. These products include newer technology.\r\nIf you use Norton AntiVirus 2005, Symantec AntiVirus Corporate Edition 9.0, or earlier products,\r\nLiveUpdate definitions are updated weekly. The exception is major outbreaks, when definitions are\r\nupdated more often.\r\nDownloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are\r\nposted daily. You should download the definitions from the Symantec Security Response Web site and\r\nmanually install them.\r\nhttps://web.archive.org/web/20190508170055/https://www.symantec.com/security-center/writeup/2000-122010-2655-99\r\nPage 4 of 5\n\nThe latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions . For\r\ndetailed instructions read the document: How to update virus definition files using the Intelligent Updater .\r\n3. To run a full system scan\r\n1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.\r\nFor Norton AntiVirus consumer products: Read the document: How to configure Norton AntiVirus to scan\r\nall files.\r\nFor Symantec AntiVirus Enterprise products: Read the document: How to verify that a Symantec Corporate\r\nantivirus product is set to scan all files.\r\n2. Run a full system scan.\r\n3. If any files are detected, follow the instructions displayed by your antivirus program.\r\nImportant: If you are unable to start your Symantec antivirus product or the product reports that it cannot delete a\r\ndetected file, you may need to stop the risk from running in order to remove it. To do this, run the scan in Safe\r\nmode. For instructions, read the document, How to start the computer in Safe Mode . Once you have restarted in\r\nSafe mode, run the scan again.\r\nAfter the files are deleted, restart the computer in Normal mode.\r\nWriteup By: Motoaki Yamamura\r\nSource: https://web.archive.org/web/20190508170055/https://www.symantec.com/security-center/writeup/2000-122010-2655-99\r\nhttps://web.archive.org/web/20190508170055/https://www.symantec.com/security-center/writeup/2000-122010-2655-99\r\nPage 5 of 5",
	"extraction_quality": 1,
	"language": "EN",
	"sources": [
		"MITRE"
	],
	"origins": [
		"web"
	],
	"references": [
		"https://web.archive.org/web/20190508170055/https://www.symantec.com/security-center/writeup/2000-122010-2655-99"
	],
	"report_names": [
		"2000-122010-2655-99"
	],
	"threat_actors": [],
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	"ts_updated_at": 1775826700,
	"ts_creation_date": 0,
	"ts_modification_date": 0,
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