Cryptojacking: When Hackers Mine Crypto on Your Computers

Your computers have been sluggish lately. Fans are running louder than usual. Electricity bills have crept up. Your team chalks it up to aging hardware or a need for new machines. But there is another possibility that most small business owners never consider: someone might be using your computers to mine cryptocurrency — and pocketing the profits.

flowchart LR
    A["Malicious Script Injected"] --> B["Runs on Victim Device"]
    B --> C["Mines Cryptocurrency"]
    C --> D["CPU Usage Spikes"]
    D --> E["Performance Degrades"]
    E --> F["Higher Energy Costs"]
  

This is cryptojacking, and it is one of the most overlooked cybersecurity threats facing small businesses today. Unlike ransomware, which announces itself loudly, cryptojacking is designed to operate in silence for as long as possible. The longer it goes undetected, the more money the attacker makes.

What Is Cryptojacking?

Cryptocurrency mining is the process of using computer processing power to solve complex mathematical problems that verify cryptocurrency transactions. Miners are rewarded with cryptocurrency for this work. The catch is that mining requires significant computing power and electricity — and those costs eat into the profits.

Cryptojacking solves this problem for criminals by shifting those costs to you. Attackers install mining software on your computers, servers, or even your website, using your hardware and your electricity bill to generate cryptocurrency that goes straight to their digital wallet.

The economics are simple: the attacker pays nothing for the computing power and energy, so every coin mined is pure profit. Meanwhile, your business absorbs the costs through slower computers, higher energy bills, and accelerated hardware wear.

Cryptojacking is the digital equivalent of someone breaking into your office at night, plugging in their equipment, and running up your electric bill — except they never have to physically enter the building.

How Cryptojacking Infects Your Systems

There are several ways cryptojacking malware can end up on your business systems:

Malware-Based Cryptojacking

The most persistent form involves malware installed directly on your computers. This typically arrives through phishing emails with malicious attachments, infected software downloads, or exploited vulnerabilities in your systems. Once installed, the mining software runs continuously in the background, often surviving reboots and hiding from basic security scans.

Browser-Based Cryptojacking

Some attacks run mining code directly in web browsers. An employee visits a compromised or malicious website, and JavaScript code begins using their computer's processor to mine cryptocurrency. This type stops when the browser tab is closed, but sophisticated versions can keep hidden browser windows running in the background. Practicing safe browsing habits can help reduce this risk.

Cloud Infrastructure Cryptojacking

If your business uses cloud services like AWS, Azure, or Google Cloud, attackers who gain access to your cloud accounts can spin up powerful virtual machines for mining. This results in massive unexpected cloud bills — sometimes tens of thousands of dollars — before the breach is discovered.

Network Device Cryptojacking

Routers, network-attached storage devices, and even smart office equipment can be hijacked for mining. These devices often have weaker security than workstations and are rarely monitored for unusual activity.

The Real Cost to Your Business

Because cryptojacking does not steal data or lock files, some business owners dismiss it as a minor nuisance. That is a mistake. The costs are real and add up quickly:

• Reduced productivity — mining consumes 50-100% of available CPU power, making computers painfully slow for employees trying to do their work
• Higher energy costs — computers running at full capacity consume significantly more electricity, and across an entire office, this adds up
• Hardware damage — sustained high CPU usage generates excessive heat, shortening the lifespan of processors, fans, and other components
• Increased IT costs — troubleshooting performance issues, replacing prematurely worn hardware, and eventually discovering and cleaning the infection
• Cloud billing shocks — cloud-based cryptojacking can generate bills in the thousands before anyone notices
• Security compromise — if cryptojacking malware is present, it means your systems are already compromised, and the attacker could deploy additional threats at any time

A study by cybersecurity researchers found that cryptojacking costs businesses an average of 50% more in electricity than the cryptocurrency the attacker earns. The victim always loses more than the attacker gains.

Warning Signs of Cryptojacking

Cryptojacking is designed to be stealthy, but it cannot completely hide its impact on system performance. Watch for these indicators:

1. Consistently slow computer performance — especially when the employee is not running demanding applications
2. Fans running loudly or constantly — mining pushes CPUs to their limits, generating heat that triggers cooling fans
3. Computers overheating — devices that are warm or hot to the touch even during light use
4. Higher than expected electricity bills — a sudden or gradual unexplained increase
5. Battery drain on laptops — batteries depleting much faster than normal
6. Slow network performance — mining malware communicates with mining pools, consuming bandwidth
7. High CPU usage in Task Manager — CPU consistently running at high percentages without a clear reason
8. Unexpected cloud computing charges — spikes in cloud service bills you cannot account for

If multiple employees report these symptoms simultaneously, cryptojacking should be high on your list of suspects.

How to Protect Your Business

Preventing and detecting cryptojacking requires a combination of endpoint protection, network monitoring, and employee awareness.

Deploy Modern Endpoint Security

Traditional antivirus may not catch all cryptojacking malware, especially newer variants. Modern endpoint security solutions use behavioral detection to identify mining activity based on how software uses system resources, not just by matching known malware signatures. Look for solutions that specifically flag cryptocurrency mining behavior.

Use Browser Extensions to Block Mining Scripts

Browser extensions like minerBlock or No Coin can detect and block JavaScript-based mining scripts. Consider deploying these across all company browsers. Some ad blockers also include cryptocurrency mining protection.

Monitor System Performance

Establish baseline performance metrics for your computers and set up alerts for sustained high CPU usage. Simple system monitoring tools can notify your IT team when a computer's processor runs at high capacity for extended periods without explanation.

Keep Software Updated

Many cryptojacking infections exploit known vulnerabilities in operating systems, browsers, and network equipment. Regular updates close these entry points. Pay particular attention to router and network device firmware, which is frequently overlooked.

Secure Cloud Accounts

If your business uses cloud infrastructure, implement strong access controls, enable multi-factor authentication, and set up billing alerts. Configure alerts for unusual resource usage — a sudden spike in CPU utilization across cloud instances is a red flag for cryptojacking.

Restrict Unnecessary Software Installation

Prevent employees from installing unauthorized software on company devices. Application whitelisting ensures that only approved programs can run, blocking cryptojacking malware even if it reaches a device.

Monitor Network Traffic

Cryptojacking malware needs to communicate with mining pools — external servers that coordinate mining activity. Network monitoring tools can identify these connections and block them. DNS filtering can also prevent devices from reaching known mining pool domains.

What to Do If You Discover Cryptojacking

If you suspect or confirm that cryptojacking malware is running on your systems, take these steps:

1. Identify affected systems — check all computers, servers, and cloud instances for signs of mining activity
2. Isolate infected machines — disconnect affected devices from the network to prevent spread and stop the mining communication
3. Run thorough malware scans — use your endpoint security tool to scan all systems, not just the ones showing symptoms
4. Check for persistence mechanisms — mining malware often installs itself to restart after reboots, check startup programs, scheduled tasks, and services
5. Investigate the entry point — determine how the malware got in to prevent reinfection, check email logs, browser history, and recent software installations
6. Update and patch — close any vulnerabilities that may have been exploited
7. Monitor for recurrence — cryptojacking operators often try again once discovered, maintain heightened monitoring for several weeks
8. Review cloud billing — if you use cloud services, audit recent charges for unauthorized resource usage

Actionable Next Steps

Cryptojacking may not make headlines like ransomware, but its quiet drain on your business resources and its indication of deeper security problems make it a threat worth taking seriously. Here is your action plan:

• Check Task Manager or Activity Monitor on several office computers right now — look for unexplained high CPU usage
• Evaluate whether your current endpoint protection can detect cryptocurrency mining behavior
• Install browser-based mining blockers on all company devices
• Set up billing alerts on all cloud service accounts with thresholds that will catch unusual spikes
• Review your electricity bills for the past few months — any unexplained increases?
• Ensure all operating systems, browsers, and network equipment firmware are up to date
• Add cryptojacking awareness to your next security training session — employees who know the symptoms can help you catch it faster

The silent nature of cryptojacking means it could be running on your systems right now without anyone knowing. A few minutes of investigation today could save your business months of stolen resources and the deeper security risks that come with an already-compromised network.