Tips to Remove Cryptolocker Ransomware

Cryptolocker is a malware that made its first appearance on 5^th September 2013 & continued its attack to late May 2014. This malign Cryptolocker Ransomware gained notoriety over the past few years for stealthily infecting a system & encrypting the files.

According to the detailed research by the security analyst, the Cryptolocker Ransomware attack utilized a Trojan that fired at the computers running on Microsoft Windows & was reported to have been published on the internet on 5^th Sep’2013. It used corrupted e-mail attachments & an existing botnet named Gameover ZeuS to spread & proliferate. Upon execution, the Cryptolocker virus encrypted certain types of files stored on local & mounted network drives by using public-key cryptography. The private key for decrypting the data was stored only on the malware’s control servers.

Following the encryption of the files, the Cryptolocker Trojan called forth a message offering the victim to pay a certain amount (in bitcoin or a pre-paid cash voucher) within a stated deadline in order to decrypt the data. The message was further followed by a threat of the permanent deletion of data & private key in case the deadline passes.

Surprisingly, the treacherous malware operators offered to decrypt files & data through an online service for a considerably higher amount in bitcoin if the deadline was not met. However, the message made no suggestion about the release of encrypted content after the payment was made.

Operation Tovar: Segregation of Cryptolocker Trojan

Though Cryptolocker Trojan removal was done easily, the infected files remained encrypted & researchers found it pretty much inconvenient to decrypt.

In the late May 2014, Operation Tovar, an international collaborative operation was carried out that extirpate Gameover ZeuS botnet, which was used by the cybercriminals to distribute malware. The operation also enabled a security firm involved to acquire the database of private keys used by Cryptolocker Ransomware. Thankfully, the security firm was able to build an online tool to recover the keys & encrypted files without paying the ransom.

Though, Operation Tovar was able to put an end to Cryptolocker Trojan attack, this malicious virus paved a way for a new generation of other sophisticated & precarious cyber threats.

Cryptolocker Ransomware -Threat Behavior

Cryptolocker Ransomware that infected Microsoft Windows ranks among one of the first Ransomware Trojan. It infected over 500,000 PCs from September 2013 to May 2014. Though the virus was brought down by US authorities in late May 2014, Cryptolocker successfully spawned a few clones named CryptoWall, Crypt0L0cker & TorrentLocker.

A ZIP file for Cryptolocker attached to an e-mail arrives on the targeted system disguised as a PDF file. The Virus smartly takes the advantage of Window’s default behavior of hiding the extension from the file names.

Upon execution it creates the following file on the compromised computer:

%UserProfile%\Application Data\[RANDOM CHARACTERS].exe.

Once the executable file has been created, it creates the following registry entry to prompt its initiation every time the Windows start: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\run\”addon_v57″ = “%UserProfile%\Application Data\[RANDOM CHARACTERS].exe

Following the infection of the system, the Cryptolocker virus thoroughly searches the network, looking for files & data to encrypt. Cryptolocker uses an obnoxious method of encryption (RSA-2048 public-key cryptography) that is quite arduous to crack.

The files targeted by the Ransomware include .doc, .docx, .docm, .wps, .xls, .xlsx, .xlsb, .ppt, .pptx, .mef, .nef, .raw, .rwl, .ptx, .pem, .pfx etc.

Each encrypted file was appended with the string: .mp3

Once the files are encrypted, the Trojan locks the desktop & displays a ransom message. The ransom note prompts the system owner to pay a ransom within the deadline in order to decrypt & recover the encrypted files. The message further threats the owner that failing to make the payment will result in the permanent deletion of the private keys.

At the initial outbreak of this malicious Trojan, infected users without established backups were given the choice of paying the ransom by various methods.

Payment Methods accepted by the Trojan include:

• MoneyPak
• Paysafecard
• Ukash
• cashU
• Bitcoin

Victims have revealed that paying ransom amount did not offer any way of recovering the files, while some said that the master key to recover files that had not been backed up was to pay the ransom. Some other victims claimed paying the ransom did not always lead to the decryption of the files.

According to security analysts, cybercriminals behind Cryptolocker were successful in extorting a colossal amount of around $3 million from the victims of this Ransomware Trojan.

Spread Techniques

The cybercriminals use various strategies for malware distribution which include –

1. Software Bundling: Software bundling is the process in which a malicious program is distributed with other free software, to get an unnoticed entry into your computer system. When a user installs a free application, the malicious programs gains a front door entry with the free application, the user has downloaded. Thus, it is a good idea to keep an eye on the installation screens while installing these free applications.
2. Infected Storage Devices: Your system can also get infected by using removable media such as USB hard drives and jump drives without scanning them with an anti-virus.
3. Spam Emails – Spamming is the most economic and common method used for the distribution of such malware. The targeted users get genuine looking emails which contain .doc, .txt, and other similar attachments. These attachments can be named as anything which can grab the user’s attention and triggers him/her to open the attachment. As soon as the user opens this attachment, the malware infects the user’s computer system.
4. Malicious Websites or Malevolent Advertisements: The malicious websites are the ones which are created just for promoting the malware infections. Such websites include but are not limited to porn sites, torrent sites and other free downloading platforms. By visiting such websites, the adware infects the user’s computer without permission. Fake advertisements and updates like Flash player and windows updates which ask the user to update to the latest version are a few examples. When the users click on such links, their computer system gets infected. That is why, it is highly recommended to resist clicking on such links. Also avoid clicking on advertisements offering free stuff such as Win an iPhones, cars or free overseas trips etc.

Threat Summary

Name: Cryptolocker

Targeted Operating System: Windows

Category: Ransomware

Symptoms: User’s files are encrypted. All locked files are appended with .mp3 extension & a ransom note demanding a ransom of $300 in bitcoin prompts on the screen. These files hence cannot be accessed by the users.

How to Remove Cryptolocker Trojan from the system?

STEP A: Remove the services installed by Cryptolocker Ransomware from the System using Safe mode with Command Prompt

STEP B: Restore your system files and settings

Tips to prevent your computer system from getting infected –

1. Keeping the Operating System Updated- In order to remain protected and avoid such infections, it is recommended to keep your Operating System updated by enabling the automatic update on your system. The systems with outdated or older versions of Operating System become an easy target for the attackers.
2. Resist clicking on spam emails – One of the major techniques used for malware distribution is forwarding spam emails to the user. The system gets infected as soon as the user clicks on the attachment. These mails appear to be genuine, so be aware and resist falling for these tricks.
3. Keep an eye on third party installations- It is quite important that you take due care while installing any third party applications for they are major source of such infections. Such malware programs come bundled with the free applications thereby requiring the user to remain cautious.
4. Regular periodical backup- In order to keep your data and files safe, it is recommended to take regular back up of all your data and files either on an external drive or cloud.
5. Use Anti-Virus Protection- We strongly recommend the use of antivirus protection/internet security in your PC like Sophos and Vipre so that it remains safe.
6. Enable the Ad Blocker/Popup Blocker in your browser- Enabling the popup blocker/ ad blocker in your chosen browser will help you to stay protected from annoying adware.

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