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How to fight and avoid ransomware

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Ransomware is malicious software that cyber criminals use to hold a user’s computer or computer files for ransom, demanding payment in order for the user to get the files back. Sadly, ransomware is becoming an increasingly popular way for malware authors to extort money from companies and consumers alike, says Nathan Loftie-Eaton, security specialist at ESET South Africa.

There are a variety of ways that ransomware can get onto a person’s machine, but as always, those techniques either boil down to social engineering tactics or using software vulnerabilities to silently install on a victim’s machine.
One specific ransomware threat that has been in the news a lot lately is Cryptolocker, which has spread quickly by its perpetrators via e-mail.

You may wonder why the big fuss over this one particular ransomware family – in essence, it is because Cryptolocker’s authors have been both nimble and persistent. There has been a concerted effort to pump out new variants, keeping up with changes in protection technology, and targeting different groups over time. Initially e-mails were targeting home users, then small to medium businesses, and now they are aiming at enterprises.

The malware also spreads via Remote Desktop Protocal (RDP) ports that have been left open to the Internet, as well as by e-mail. Cryptolocker can also affect a user’s files that are on drives that are “mapped”, which is to say, they have been given a drive letter (e.g. D:, E:, F: ). This could be an external hard-drive including USB thumb drives, or it could be a folder on the network or in the Cloud. If you have, for example, your Dropbox folder mapped locally, it can encrypt those files as well.

Paying the criminals may get your data back; however, there have been plenty of cases where the decryption key has never arrived or where it has failed to properly decrypt the files. Plus, it encourages criminal behaviour! 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.

At this point, tens of thousands of machines have been affected, though it is estimated that the criminals have sent millions of e-mails. Hopefully the remainder of the recipients have simply deleted the malicious e-mails without opening them, rather than having the e-mails unopened in their in-box, waiting to unleash more pain.

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
The single biggest thing that will defeat ransomware is having a regularly updated backup. If you are attacked with ransomware you may lose the document that you started earlier in the 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. What you need is a regular backup routine, 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 ransomware frequently arrives is in a file that is named with the extension “.PDF.EXE”, counting on Window’s default behaviour 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 e-mail
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 e-mails 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 behaviour used by Cryptolocker, which is to run its executable from the App Data or Local App Data folders. If (for some reason) you have legitimate software that you know is set to run not from the usual Program Files area, but the App Data area, you will need to exclude it from this rule.

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. For instructions to do so, visit the appropriate Microsoft Knowledge Base article below:
Windows XP RDP disable
Windows 7 RDP disable
Windows 8 RDP disable

Patch or Update your software
These next two tips are more general malware-related advice, which applies equally to Cryptolocker as to any malware threat. 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.

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 behaviour. 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. 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.
If you find yourself in a position where you have already run a ransomware file without having performed any of the previous precautions, your options are quite a bit more limited. But all may not be lost. There are a few things you can do that might help mitigate the damage, particularly if the ransomware in question is Cryptolocker:

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 has finished encrypting your files. If you disconnect yourself from the network immediately, 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 distorting them all. This technique is definitely not fool proof, 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. However, all this does is it keeps you from having to pay the higher price, and it strongly advised that you do not pay the ransom.
If you are an ESET customer and you are concerned about ransomware protection or think you have been targeted by ransomware, call our customer care. They will have the latest details on how to prevent and remediate ransomware attacks.