Recently, my PC got infected with a ransomware virus, which has changed all files to extension .derp. Now, how do I change all the file extensions to their previous versions?

To revert the file extensions changed by the ransomware and potentially recover your data, you can try the following steps:

1. Identify the Ransomware: Determine the specific ransomware that encrypted your files. This can help you find specific decryption tools or solutions made available by security professionals or law enforcement agencies.

2. Backup Encrypted Files: Make a backup of all encrypted files before attempting any recovery steps. This ensures that you do not lose any data during the process.

3. Research for Possible Solutions: Look for decryptors or tools provided by cybersecurity firms that may help in recovering your files. Some ransomware variants have decryption keys available publicly that can help in file recovery.

4. Consult Online Resources: Check online resources such as the No More Ransom Project (https://www.nomoreransom.org/) or cybersecurity forums for information and tools that might help decrypt your files.

5. Avoid Paying Ransom: It is advised not to pay the ransom demanded by the cybercriminals as it does not guarantee file recovery and supports criminal activities.

6. Use Data Recovery Software: If decryption is not possible, consider using reputable data recovery software to attempt to recover your files. Tools like Recuva, EaseUS Data Recovery Wizard, or TestDisk may help you retrieve your data.

If these steps do not lead to successful recovery, unfortunately, the best course of action may be to restore your files from a backup, if you have one available.