What is cryptojacking? How to prevent, detect, and recover from it

Criminals are using ransomware-like tactics and poisoned websites to get your employees’ computers to mine cryptocurrencies. Here’s what you can do to stop it.

Cryptojacking is the unauthorized use of someone else’s computer to mine cryptocurrency. Hackers do this by either getting the victim to click on a malicious link in an email that loads cryptomining code on the computer, or by infecting a website or online ad with JavaScript code that auto-executes once loaded in the victim’s browser.

Either way, the cryptojacking code then works in the background as unsuspecting victims use their computers normally. The only sign they might notice is slower performance or lags in execution.

Why cryptojacking is on the rise

No one knows for certain how much cryptocurrency is mined through cryptojacking, but there’s no question that the practice is rampant. Browser-based cryptojacking is growing fast. In November, Adguard reported a 31 percent growth rate for in-browser cryptojacking. Its research found 33,000 websites running cryptomining scripts. Adguard estimated that those site had a billion combined monthly visitors.

“Cryptomining is in its infancy. There’s a lot of room for growth and evolution,” says Marc Laliberte, threat analyst at network security solutions provider WatchGuard. He notes that Coinhive, the most popular JavaScript miner that is also used for legitimate cryptomining activity, is easy to deploy and generated $300 thousand in its first month. “It’s grown quite a bit since then. It’s really easy money.”

In January, researchers discovered the Smominru cryptomining botnet, which infected more than a half-million machines, mostly in Russia, India, and Taiwan. The botnet targeted Windows servers to mine Monero, and cybersecurity firm Proofpoint estimated that it had generated as much as US$3.6 million in value as of the end of January.

Cryptojacking doesn’t even require significant technical skills. According to the report, The New Gold Rush Cryptocurrencies Are the New Frontier of Fraud, from Digital Shadows, cryptojacking kits are available on the dark web for as little as $30.

The simple reason why cryptojacking is becoming more popular with hackers is more money for less risk. “Hackers see cryptojacking as a cheaper, more profitable alternative to ransomware,” says Alex Vaystikh, CTO and cofounder of SecBI. With ransomware, a hacker might get three people to pay for every 100 computers infected, he explains. With cryptojacking, all 100 of those infected machines work for the hacker to mine cryptocurrency. “[The hacker] might make the same as those three ransomware payments, but cryptomining continuously generates money,” he says.

The risk of being caught and identified is also much less than with ransomware. The cryptomining code runs surreptitiously and can go undetected for a long time. Once discovered, it’s very hard to trace back to the source, and the victims have little incentive to do so since nothing was stolen or encrypted. Hackers tend to prefer anonymous cryptocurrencies like Monero and Zcash over the more popular Bitcoin because it is harder to track the illegal activity back to them.

How cryptojacking works

Hackers have two primary ways to get a victim’s computer to secretly mine cryptocurrencies. One is to trick victims into loading cryptomining code onto their computers. This is done through phishing-like tactics: Victims receive a legitimate-looking email that encourages them to click on a link. The link runs code that places the cryptomining script on the computer. The script then runs in the background as the victim works.

The other method is to inject a script on a website or an ad that is delivered to multiple websites. Once victims visit the website or the infected ad pops up in their browsers, the script automatically executes. No code is stored on the victims’ computers. Whichever method is used, the code runs complex mathematical problems on the victims’ computers and sends the results to a server that the hacker controls.

Hackers often will use both methods to maximize their return. “Attacks use old malware tricks to deliver more reliable and persistent software [to the victims’ computers] as a fall back,” says Vaystikh. For example, of 100 devices mining cryptocurrencies for a hacker, 10 percent might be generating income from code on the victims’ machines, while 90 percent do so through their web browsers.

Unlike most other types of malware, cryptojacking scripts do no damage to computers or victims’ data. They do steal CPU processing resources. For individual users, slower computer performance might be just an annoyance. Organization with many cryptojacked systems can incur real costs in terms of help desk and IT time spent tracking down performance issues and replacing components or systems in the hope of solving the problem.  

How to prevent cryptojacking

Follow these steps to minimize the risk of your organization falling prey to cryptojacking:

Incorporate the cryptojacking threat into your security awareness training, focusing on phishing-type attempts to load scripts onto users’ computers. “Training will help protect you when technical solutions might fail,” says Laliberte. He believes phishing will continue to be the primary method to deliver malware of all types.

Employee training won’t help with auto-executing cryptojacking from visiting legitimate websites. “Training is less effective for cryptojacking because you can’t tell users which websites not to go to,” says Vaystikh.

Install an ad-blocking or anti-cryptomining extension on web browsers. Since cryptojacking scripts are often delivered through web ads, installing an ad blocker can be an effective means of stopping them. Some ad blockers like Ad Blocker Plus have some capability to detect cryptomining scripts. Laliberte recommends extensions like No Coin and MinerBlock, which are designed to detect and block cryptomining scripts.

Keep your web filtering tools up to date. If you identify a web page that is delivering cryptojacking scripts, make sure your users are blocked from accessing it again.

Maintain browser extensions. Some attackers are using malicious browser extensions or poisoning legitimate extensions to execute cryptomining scripts.

Use a mobile device management (MDM) solution to better control what’s on users’ devices. Bring-your-own-device (BYOD) policies present a challenge to preventing illicit cryptomining. “MDM can go a long way to keep BYOD safer,” says Laliberte. An MDM solution can help manage apps and extensions on users’ devices. MDM solutions tend to be geared toward larger enterprises, and smaller companies often can’t afford them. However, Laliberte notes that mobile devices are not as at risk as desktop computers and servers. Because they tend to have less processing power, they are not as lucrative for the hackers.

How to detect cryptojacking

Like ransomware, cryptojacking can affect your organization despite your best efforts to stop it. Detecting it can be difficult, especially if only a few systems are compromised. Don’t count on your existing endpoint protection tools to stop cryptojacking. “Cryptomining code can hide from signature-based detection tools,” says Laliberte. “Desktop antivirus tools won’t see them.” Here’s what will work:

Train your help desk to look for signs of cryptomining. Sometimes the first indication is a spike in help desk complaints about slow computer performance, says SecBI’s Vaystikh. That should raise a red flag to investigate further.

Other signals help desk should look for might be overheating systems, which could cause CPU or cooling fan failures, says Laliberte. “Heat [from excessive CPU usage] causes damage and can reduce the lifecycle of devices,” he says. This is especially true of thin mobile devices like tablets and smartphones.

Deploy a network monitoring solution. Vaystikh believes cryptojacking is easier to detect in a corporate network than it is at home because most consumer end-point solutions do not detect it. Cryptojacking is easy to detect via network monitoring solutions, and most corporate organizations have network monitoring tools.

However, few organizations with network motoring tools and data have the tools and capabilities to analyze that information for accurate detection. SecBI, for example, develops an artificial intelligence solution to analyze network data and detect cryptojacking and other specific threats.

Laliberte agrees that network monitoring is your best bet to detect cryptomining activity. “Network perimeter monitoring that reviews all web traffic has a better chance of detecting cryptominers,” he says. Many monitoring solutions drill down that activity to individual users so you can identify which devices are affected.

How to respond to a cryptojacking attack

Kill and block website-delivered scripts. For in-browser JavaScript attacks, the solution is simple once cryptomining is detected: Kill the browser tab running the script. IT should note the website URL that’s the source of the script and update the company’s web filters to block it. Consider deploying anti-cryptomining tools to help prevent future attacks.

Update and purge browser extensions. “If an extension infected the browser, closing the tab won’t help,” says Laliberte. “Update all the extensions and remove those not needed or that are infected.”

Learn and adapt. Use the experience to better understand how the attacker was able to compromise your systems. Update your user, helpdesk and IT training so they are better able to identify cryptojacking attempts and respond accordingly.

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