CryptoLocker Ransomware: What it is, warning signs, and how to recover safely

CryptoLocker Ransomware

What it is

CryptoLocker is ransomware that breaks into a Windows PC, hunts for documents (on the computer and connected drives), encrypts them with strong keys, and then demands a payment to unlock your files. You’ll see a ransom note saying your data is locked and a deadline is ticking.

What you may notice

  • Files won’t open and may have new extensions

  • A ransom message on the desktop or in many folders

  • Backups on attached or network drives also unusable

  • Security tools disabled; sudden spikes in CPU/disk activity

If it hits (act fast)

  1. Isolate the PC (unplug network/Wi-Fi; disconnect external drives).

  2. Don’t delete ransom notes or logs—they can help recovery.

  3. Check for offline backups; rebuild the system clean and restore data.

  4. From a clean device, change passwords (email/admin) and enable MFA.

  5. Ask IT/IR to identify the entry point and block related domains/IPs.

Prevent it

  • Keep Windows and apps patched; remove or lock down remote access (RDP/VPN).

  • Use reputable EDR/anti-malware and email filtering.

  • Maintain offline, tested backups (and practice restores).

  • Train users to spot phishing and fake updates.

  • Use least privilege and MFA for all important accounts.

    Glossary (A–Z)

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