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Recommended Practices:  Dealing with CryptoLocker

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This is a multi-part series on recommended IT practices for organizations and their end-users.  Additional parts will be included in upcoming newsletters.

CryptoLocker surfaced in the fall of 2013; it is a ransomware trojan that, upon activation, encrypts all data files to which the infected end-user has read-write access, and then demands payment to decrypt.  It typically hides as an attachment within a phishing email and can even work over a home user’s VPN connection to encrypt data files on the organizations’ server(s).

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The cyber-criminal’s intent is to receive untraceable payment via cyber-currency in exchange for a decryption key to unlock the data files, forming a one-to-one relationship between the cyber-criminal and the infected user:  The cyber-criminal knows the user is infected and awaits payment; if thwarted in his/her extortion attempt, that information is retained by the cyber-criminal, which could reduce future efforts to pursue your organization.

Of greater concern; if an individual or organization pays the ransom, that information is also known, recorded, and potentially shared for future attempts.  Basically, if you pay the ransom, you may be targeted for new efforts.

The cyber-criminal is likely acting within a crime syndicate; he/she might not even be technically savvy since CryptoLocker tools are readily available and easy to use.

We have recently seen a significant upswing in CryptoLocker attempts; the source emails spoof the email addresses of known parties while the attachment might carry a seemingly harmless “PDF” extension.  The message is compelling; an end-user unwittingly clicks the attachment and starts the process.

The first best step is prevention:

  • If feasible, use group policies or AppLocker to restrict software execution1
  • Limit access only to needed files; make them read-only where appropriate
  • Update security patches on all operating systems and end-user applications2
  • Deploy and continually update anti-malware apps on all end-user devices2
  • Deploy a robust, anti-spam solution that can block executables2
  • Consider blocking or quarantining all incoming attachments
  • Setup a backup routine that addresses data files frequently3

For more information, Jonathan Haskell of ComputerWorld reviews group policy restrictions in his article:  “CryptoLocker:  How to avoid getting infected and what to do if you are”.  Also, Third Tier and SMB Kitchen have jointly released a CryptoLocker Prevention Kit to assist in developing these group policies.

Education is also critical4:

  • Schedule regular training reviews with your end-users
  • Demonstrate to your end-users how to spot potential threats
  • Discuss the dangers of clicking attachments, even those from known sources

If you are infected by CryptoLocker5:

  • Identify the infected computer and remove it from the network
  • To be prudent, change online and system passwords
  • Create forensic images of infected computers
  • Preserve all firewall, Intrusion Prevention, and Active Directory logs for potential analysis by law-enforcement officials

Index of referenced articles:

1 See the January 2015 Bryley Tips and Information article: Recommended Practices:  Manage End Users via Active Directory and the February issue for the article: Recommended Practices – Part 7:  Resource Management via Active Directory.

2 See the June 2015 Bryley Tips and Information article:  Recommended Practices:  IT security cheat-sheet.

3 See the April issue of Bryley Tips and Information for Bryley Basics:  How ransomware (CryptoLocker) makes backups more critical.

4 See the May 2015 Bryley Tips and Information article: Recommended Practices: Basic IT training for end users

5 View detailed prevention and response techniques in CryptoLocker Prevention and Remediation Techniques, presented by fishnet™ security.

Bryley Basics: How ransomware (Crypto Locker) makes backups more critical

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Ransomware – usually Crypto Locker and its variants – is a form of cyber-malware based on encryption software that seeks payment (ransom) to undo the damage; when infected, the malware typically encrypts all data files, rendering them useless until the ransom is paid.  (Encryption software scrambles a files’ contents and creates an encryption key, essentially a code used to reverse the process.  Unless you have this key and the encryption software, the files remain unreadable.)

Hiawatha Bray of the Boston Globe recently reported a ransomware infection at the Tewksbury Police Department; after repeated attempts to decrypt, the Chief of Police paid the ransom.

Other than paying the ransom, which is risky and not recommended since it potentially makes you more of a target in the future, the only way to thwart ransomware is by restoring the corrupted files through a backup that was created before the infection.

A properly planned and implemented backup process is vital since data stored on a network server represents many hours of effort over time, making it impractical and usually impossible to recreate.  A properly functioning, multi-point-in-time backup is necessary to provide restoration under these and other scenarios:

  • A server fails
  • A file is deleted
  • A template is written over
  • An application upgrade fails and must be restored
  • A document is inadvertently changed and saved by a user

A backup should be a complete, recoverable copy of not just data, but the entire server/network environment.  It should have these properties:

  • Sequenced over many days
  • Complete image
  • Offsite storage

For information on backups, visit our Data-Backup Guidelines.

CryptoLocker Case Study

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The following event depicts a real-life malware attack that infected a New England manufacturing firm. The company has chosen to share its story anonymously to help other businesses avoid a similar fate.

The unsuspecting sales rep certainly reacted in a way anyone would expect. He received an email with a voicemail attachment that looked like it came from the company CEO. When the CEO calls, reps jump to attention, and at this particular manufacturing firm based in New England, the business relies on a communication system that sends voicemails as email attachments. So the sales rep had no reason to suspect anything was wrong.

As it turns out, something was very wrong.

Click the link below to read the full article.

Bryley — CryptoLocker Remediation — 2013

Beware CryptoLocker

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We have seen a rise in CryptoLocker virus attacks; these attacks can cripple the data files on your computer and on your computer network.

CryptoLocker is a destructive, ransomware virus; once downloaded, it locates and encrypts data files, which renders them inaccessible.  CryptoLocker does not announce its presence until all data files (Microsoft Office files, PDF files, etc.) are encrypted; it then asks for payment (ransom) to unencrypt these files.  (This type of ransomware is called “cryptoviral extortion”.)

The usual virus-delivery method is via email; the email looks legitimate and includes an attachment.  Once the attachment is clicked, the virus starts and then continues until all data files are encrypted or until the computer is powered-down.

You will not be able to unencrypt these files.  There is no cure.  There is no fix.

If the infected computer is connected to a computer network, data files on other computers and/or on the server(s) may also be encrypted and made inoperable.

Although payment is demanded to unencrypt the files, it should not be sent since any type of response to these criminals could open your computer network to future attacks.  The only recommended recovery method is to restore the encrypted data files from the latest backup.

Please visit http://www.bleepingcomputer.com/virus-removal/cryptolocker-ransomware-information for more information on CryptoLocker.

Mike Morel, Engineer at Bryley Systems, suggests adopting these practices to reduce the risk of activating the CryptoLocker virus on your computer:

  • Do not open attachments within emails from sources that look legitimate, but are unexpected.
  • If you are expecting an attachment from someone, save the attachment first (without opening it) and then scan the attachment with your malware and anti-virus scanners before opening it.
  • Backup all data files regularly.

If you discover this virus, please immediately power-down the offending computer; if it is connected to a computer server, shutdown the computer network.  Then, call Bryley Systems at 978.562.6077 and select option one for technical support.

For additional information, see our lead article “Cybercrime targets smaller organizations” from the September 2012 edition of Bryley Tips and Information at

https://www.bryley.com/news/newsletter/bryley-tips-and-information-september-2012/.