Ransomware: How to stay safe
Ransomware is malware that holds the victim’s computer to ransom, either by restricting access to the computer by locking the desktop or by encrypting the user’s files. The malware then displays a ransom note, often claiming to be from the police, the FBI, or some other type of law enforcement agency. Ransomware can even tell what country you’re in and display a ransom note that looks like it’s from your local police force. The ransom note may claim that the computer was used to look at illegal websites, videos, or images and will try to frighten the victim into paying up by threatening to bring them to court. Victims are often too embarrassed to ask for help because the ransom note may say they were viewing pornographic content.
There are two types of ransomware in circulation:
- Encrypting ransomware, which incorporates advanced encryption algorithms. It’s designed to block system files and demand payment to provide the victim with the key that can decrypt the blocked content. Examples include CryptoLocker, Locky, CrytpoWall and more. One specific ransomware threat that has been in the news a lot lately is Cryptolocker (detected by ESET as Win32/Filecoder -check the ESET Knowledge Base for updated information on detection of Cryptolocker and other ransomware). The perpetrators of Cryptolocker have been emailing it to huge numbers of people, targeting particularly the US and UK. Like a notorious criminal, this malware has been associated with a variety of other bad actors – backdoor Trojans, downloaders, spammers, password-stealers, ad-clickers and the like. Cryptolocker may come on its own (often by email) or by way of a backdoor or downloader, brought along as an additional component.
- Locker ransomware, which locks the victim out of the operating system, making it impossible to access the desktop and any apps or files. The files are not encrypted in this case, but the attackers still ask for a ransom to unlock the infected computer. Examples include the police-themed ransomware or Winlocker.
- Another version pertaining to this type is the Master Boot Record (MBR) ransomware. The MBR is the section of a PC’s hard drive which enables the operating system to boot up. When MBR ransomware strikes, the boot process can’t complete as usual, and prompts a ransom note to be displayed on the screen. Examples include Satana and Petya ransomware.
However, the most widespread type of ransomware is crypto-ransomware or encrypting ransomware, which I’ll focus on in this guide. The cyber security community agrees that this is the most prominent and worrisome cyber threat of the moment.
Ransomware has some key characteristics that set it apart from other malware:
- It features unbreakable encryption, which means that you can’t decrypt the files on your own (there are various decryption tools released by cyber security researchers – more on that later);
- It has the ability to encrypt all kinds of files, from documents to pictures, videos, audio files and other things you may have on your PC;
- It can scramble your file names, so you can’t know which data was affected. This is one of the social engineering tricks used to confuse and coerce victims into paying the ransom;
- It will add a different extension to your files, to sometimes signal a specific type of ransomware strain;
- It will display an image or a message that lets you know your data has been encrypted and that you have to pay a specific sum of money to get it back;
- It requests payment in Bitcoins, because this crypto-currency cannot be tracked by cyber security researchers or law enforcements agencies;
- Usually, the ransom payments have a time-limit, to add another level of psychological constraint to this extortion scheme. Going over the deadline typically means that the ransom will increase, but it can also mean that the data will be destroyed and lost forever.
- It uses a complex set of evasion techniques to go undetected by traditional antivirus (more on this in the “Why ransomware often goes undetected by antivirus” section);
- It often recruits the infected PCs into botnets, so cyber criminals can expand their infrastructure and fuel future attacks;
- It can spread to other PCs connected in a local network, creating further damage;
- It frequently features data exfiltration capabilities, which means that ransomware can extract data from the affected computer (usernames, passwords, email addresses, etc.) and send it to a server controlled by cyber criminals;
- It sometimes includes geographical targeting, meaning the ransom note is translated into the victim’s language, to increase the chances for the ransom to be paid.
What can you do about it?
On the one hand, ransomware can be very scary – the encrypted files can essentially be considered damaged beyond repair. But if you have properly prepared your system, it is really nothing more than a nuisance. Here are a few tips that will help you keep ransomware from wrecking your day:
- Back up your data
The single biggest thing that will defeat ransomware is having a regularly updated backup. If you are attacked with ransomware you may lose that document you started earlier this morning, but if you can restore your system to an earlier snapshot or clean up your machine and restore your other lost documents from backup, you can rest easy. Remember that Cryptolocker will also encrypt files on drives that are mapped. This includes any external drives such as a USB thumb drive, as well as any network or cloud file stores that you have assigned a drive letter. So, what you need is a regular backup regimen, to an external drive or backup service, one that is not assigned a drive letter or is disconnected when it is not doing backup.
- Show hidden file-extensions
One way that Cryptolocker frequently arrives is in a file that is named with the extension “.PDF.EXE”, counting on Window’s default behavior of hiding known file-extensions. If you re-enable the ability to see the full file-extension, it can be easier to spot suspicious files.
- Filter EXEs in email
If your gateway mail scanner has the ability to filter files by extension, you may wish to deny mails sent with “.EXE” files, or to deny mails sent with files that have two file extensions, the last one being executable (“*.*.EXE” files, in filter-speak). If you do legitimately need to exchange executable files within your environment and are denying emails with “.EXE” files, you can do so with ZIP files (password-protected, of course) or via cloud services.
- Disable files running from AppData/LocalAppData folders
You can create rules within Windows or with Intrusion Prevention Software, to disallow a particular, notable behavior used by Cryptolocker, which is to run its executable from the App Data or Local App Data folders.
- Use the Cryptolocker Prevention Kit
The Cryptolocker Prevention Kit is a tool created by Third Tier that automates the process of making a Group Policy to disable files running from the App Data and Local App Data folders, as well as disabling executable files from running from the Temp directory of various unzipping utilities. This tool is updated as new techniques are discovered for Cryptolocker, so you will want to check in periodically to make sure you have the latest version. If you need to create exemptions to these rules, they provide this document that explains that process.
- Disable RDP
The Cryptolocker/Filecoder malware often accesses target machines using Remote Desktop Protocol (RDP), a Windows utility that allows others to access your desktop remotely. If you do not require the use of RDP, you can disable RDP to protect your machine from Filecoder and other RDP exploits.
- Patch or Update your software
Malware authors frequently rely on people running outdated software with known vulnerabilities, which they can exploit to silently get onto your system. It can significantly decrease the potential for ransomware-pain if you make a practice of updating your software often. Some vendors release security updates on a regular basis (Microsoft and Adobe both use the second Tuesday of the month), but there are often “out-of-band” or unscheduled updates in case of emergency. Enable automatic updates if you can, or go directly to the software vendor’s website, as malware authors like to disguise their creations as software update notifications too.
- Use a reputable security suite
It is always a good idea to have both anti-malware software and a software firewall to help you identify threats or suspicious behavior. Malware authors frequently send out new variants, to try to avoid detection, so this is why it is important to have both layers of protection. And at this point, most malware relies on remote instructions to carry out their misdeeds. If you run across a ransomware variant that is so new that it gets past anti-malware software, it may still be caught by a firewall when it attempts to connect with its Command and Control (C&C) server to receive instructions for encrypting your files.
- Disconnect from WiFi or unplug from the network immediately
If you run a file that you suspect may be ransomware, but you have not yet seen the characteristic ransomware screen, if you act very quickly you might be able to stop communication with the C&C server before it finish encrypting your files. If you disconnect yourself from the network immediately (have I stressed enough that this must be done right away?), you might mitigate the damage. It takes some time to encrypt all your files, so you may be able to stop it before it succeeds in garbling them all. This technique is definitely not foolproof, and you might not be sufficiently lucky or be able to move more quickly than the malware, but disconnecting from the network may be better than doing nothing.
- Use System Restore to get back to a known-clean state
If you have System Restore enabled on your Windows machine, you might be able to take your system back to a known-clean state. But, again, you have to out-smart the malware. Newer versions of Cryptolocker can have the ability to delete “Shadow” files from System Restore, which means those files will not be there when you try to replace your malware-damaged versions. Cryptolocker will start the deletion process whenever an executable file is run, so you will need to move very quickly as executables may be started as part of an automated process. That is to say, executable files may be run without you knowing, as a normal part of your Windows system’s operation.
- Set the BIOS clock back
Cryptolocker has a payment timer that is generally set to 72 hours, after which time the price for your decryption key goes up significantly. (The price may vary as Bitcoin has a fairly volatile value. At the time of writing the initial price was .5 Bitcoin or $300, which then goes up to 4 Bitcoin) You can “beat the clock” somewhat, by setting the BIOS clock back to a time before the 72-hour window is up.
Paying the criminals may get your data back, but there have been plenty of cases where the decryption key never arrived or where it failed to properly decrypt the files. Plus, it encourages criminal behavior! Ransoming anything is not a legitimate business practice, and the malware authors are under no obligation to do as promised – they can take your money and provide nothing in return, because there is no backlash if the criminals fail to deliver.