As a desktop support engineer, you can follow these steps to troubleshoot virus and malware infections on a desktop computer:

1. Run an antivirus scan: Use a reputable antivirus software to perform a full system scan and remove any detected viruses or malware.
2. Update the antivirus software: Ensure that the antivirus software is up to date to ensure that it can detect the latest threats.
3. Disable system restore: Disabling system restore can prevent the virus or malware from being restored after it has been removed.
4. Run a malware scanner: In addition to an antivirus scan, run a malware scanner such as Malwarebytes Anti-Malware to detect and remove any additional malware.
5. Check for malicious extensions: Check the extensions in your web browser for any that you don’t recognize or that are known to be malicious. Remove any suspicious extensions.
6. Remove suspicious programs: Check the list of installed programs for any that you don’t recognize or that are known to be malicious. Uninstall any suspicious programs.
7. Check for malicious files: Use a tool like Microsoft Defender Offline to scan for and remove any malicious files that may be hidden on the computer.
8. Change passwords: Change passwords for any accounts that may have been compromised by the virus or malware.
9. Keep software and operating system up to date: Make sure that all software and the operating system are up to date to ensure that they are protected against known threats.

It’s important to regularly backup important data to protect against data loss from virus or malware infections.