Detail the steps to perform a thorough malware removal from an infected system, including using specialized tools, identifying rootkits, and verifying the system's integrity after cleaning.
Performing thorough malware removal requires a systematic approach involving specialized tools, careful analysis, and verification steps to ensure the system's integrity. Here's a detailed guide:
1. Preparation and Initial Assessment:
- Disconnect from the Network: Immediately disconnect the infected system from the network (both wired and wireless) to prevent the malware from spreading to other devices or communicating with its command-and-control server.
- Identify Symptoms: Document the symptoms of the infection, such as slow performance, unusual pop-ups, unauthorized network activity, or file encryption.
- Backup Important Data (If Possible): If the system is still somewhat functional, attempt to back up important data to an external drive. However, be cautious not to back up any potentially infected files. Consider using a bootable antivirus rescue disk to perform the backup in a clean environment.
- Gather Information: Note the operating system version, installed software, and any recent changes made to the system. This information can help in identifying the source of the infection and selecting the appropriate removal tools.
- Create a Bootable Rescue Media: Download and create a bootable antivirus rescue disk from a trusted antivirus vendor (e.g., Kaspersky Rescue Disk, Bitdefender Rescue Environment). This will allow you to scan and clean the system from a clean environment without loading the infected operating system.
2. Booting from Rescue Media:
- Change Boot Order: Power off the infected system and boot from the bootable rescue media. You may need to change the boot order in the BIOS/UEFI settings to prioritize the USB drive or DVD.
- Start the Antivirus Scanner: Once the system boots from the rescue media, launch the antivirus scanner.
3. Scanning for Malware:
- Perform a Full System Scan: Run a full system scan with the antivirus scanner. This will scan all files and directories on the hard drive for malware.
- Enable Rootkit Scanning: Ensure that the antivirus scanner is configured to scan for rootkits. Rootkits are a type of malware that hides its presence from the operating system and antivirus software.
- Update Virus Definitions: Before starting the scan, update the virus definitions to ensure that the scanner has the latest information about known malware threats.
- Quarantine Infected Files: Configure the antivirus scanner to automatically quarantine any infected files. Quarantining moves the files to a safe location where they cannot harm the system.
- Analyze Scan Results: After the scan completes, review the results. Pay close attention to any files that were identified as malware.
4. Removing Malware:
- Delete Quarantined Files: After reviewing the scan results, delete the quarantined files to permanently remove the malware from the system.
- Use Specialized Removal Tools: For stubborn or complex malware infections, use specialized removal tools designed for specific types of malware. These tools can often remove malware that antivirus scanners may miss.
- Examples:
- Malwarebytes Anti-Rootkit: Removes rootkits and other hidden malware.
- AdwCleaner: Removes adware and browser hijackers.
- RKill: Terminates known malware processes.
- Run Multiple Scans: Run multiple scans with different antivirus scanners and removal tools to ensure that all malware is removed.
5. Identifying and Removing Rootkits:
- Use Rootkit Scanners: Use specialized rootkit scanners to identify and remove rootkits. Some antivirus scanners have built-in rootkit scanning capabilities, but dedicated rootkit scanners are often more effective.
- Examples:
- GMER: Detects and removes rootkits.
- Sophos Rootkit Removal: Removes various types of rootkits.
- Manual Rootkit Removal (Advanced): In some cases, manual rootkit removal may be necessary. This involves using system utilities to identify and remove rootkit files, registry entries, and processes. This is an advanced technique that should only be performed by experienced users.
- Steps:
- Identify Suspicious Processes: Use Process Explorer to identify suspicious processes that are running on the system. Look for processes with unusual names, high CPU usage, or hidden modules.
- Examine Registry Entries: Use Registry Editor to examine the registry for suspicious entries. Look for entries that have been added or modified by the rootkit.
- Delete Rootkit Files: Use a file manager to delete any rootkit files that you have identified.
- Be Extremely Careful: Incorrect manual removal can damage the OS.
6. Repairing System Files:
- Run System File Checker (SFC): After removing the malware, run the System File Checker (SFC) utility to scan for and repair any corrupted system files.
- Open Command Prompt as an administrator.
- Type the following command and press Enter:
```
sfc /scannow
```
- Use DISM: If SFC cannot repair the corrupted system files, use the Deployment Image Servicing and Management (DISM) tool to repair the Windows Component Store.
- Open Command Prompt as an administrator.
- Type the following command and press Enter:
```
DISM /Online /Cleanup-Image /RestoreHealth
```
- Repair Boot Sector: If the boot sector has been infected, use the Bootrec.exe tool to repair it.
- Boot from Windows installation media.
- Select "Repair your computer."
- Select "Troubleshoot" -> "Advanced options" -> "Command Prompt."
- Type the following commands and press Enter after each command:
```
bootrec /fixmbr
bootrec /fixboot
bootrec /rebuildbcd
```
7. Restoring System Settings:
- Review Startup Programs: Check the list of programs that start automatically with Windows and disable any suspicious or unnecessary programs.
- Use Task Manager (Startup tab) or Autoruns to review startup programs.
- Reset Browser Settings: Reset the browser settings to their default values to remove any unwanted toolbars, extensions, or search engine redirects.
- Check DNS Settings: Ensure that the DNS settings are configured correctly and that there are no malicious DNS servers configured.
- Open Network Connections.
- Right-click on the network adapter and select "Properties."
- Select "Internet Protocol Version 4 (TCP/IPv4)" and click "Properties."
- Verify that the DNS server addresses are correct.
- Remove Temporary Files: Delete temporary files and folders to remove any remnants of the malware.
- Use Disk Cleanup to remove temporary files.
8. Updating Software and Security Settings:
- Install Security Updates: Install all available security updates for Windows and other software.
- Update Antivirus Software: Update the antivirus software to the latest version.
- Enable Firewall: Ensure that the Windows Firewall is enabled and configured correctly.
- Configure User Account Control (UAC): Set the UAC settings to a high level to prompt for elevation for most actions.
9. Verifying System Integrity:
- Monitor System Performance: Monitor the system performance for any unusual activity.
- Check Network Connections: Check the network connections for any unauthorized connections.
- Scan with Multiple Tools: Run multiple scans with different antivirus scanners and removal tools to verify that all malware has been removed.
- Perform a Clean Boot: Perform a clean boot to start Windows with a minimal set of drivers and startup programs. This can help identify any remaining conflicts or issues.
- Consider a Clean Installation: If you are still concerned about the system's integrity, consider performing a clean installation of Windows. This will erase all data on the system drive and install a fresh copy of Windows.
- Review Logs: Check event logs for any unusual or suspicious activity.
10. Post-Removal Actions:
- Change Passwords: Change all passwords for important accounts, such as email, banking, and social media accounts.
- Inform Affected Parties: If the malware infection may have compromised other systems or data, inform the affected parties.
- Educate Users: Educate users about the dangers of malware and how to prevent infections.
- Implement Security Policies: Implement security policies to prevent future infections.
Example Scenario:
- A user's computer is infected with ransomware that has encrypted their files.
- Steps:
- Disconnect the computer from the network.
- Boot from a bootable antivirus rescue disk.
- Scan the system for malware and remove any infected files.
- Use a specialized ransomware removal tool to decrypt the encrypted files (if available).
- Run SFC and DISM to repair any corrupted system files.
- Reset browser settings and remove temporary files.
- Update Windows and antivirus software.
- Verify the system's integrity by running multiple scans.
- Change passwords for all important accounts.
By following these steps, you can perform a thorough malware removal from an infected system and restore its integrity. Remember to be patient and persistent, as some malware infections can be difficult to remove.