How Black Hat Hackers Sneak Malicious Code into Images

Hiding malicious code inside images isn’t a new trick, but cybercriminals are constantly refining their methods. They’ve learned how to sneak harmful scripts into everyday file types—emails, PDFs, Excel spreadsheets, and even seemingly harmless PNG and JPG images.

But here’s the alarming part: hackers aren’t just sticking to old techniques. They’re evolving. They’re embedding even more dangerous malware into images, making their attacks harder to detect and stop.

Some of the most notorious cyber threats—Keylogger, 0bj3ctivityStealer, and Lumma Stealer—are now being spread through infected images. This method is gaining traction, turning pictures into Trojan horses for cybercrime.

With insights from the HP Wolf Security Threat Insights Report, Techopedia takes a closer look at how hackers craft these deceptive images and the risks they pose.

A picture may be worth a thousand words, but sometimes, it’s hiding a silent threat.

Key Takeaways:

Hackers are embedding malicious code into images to bypass security filters and spread malware, using techniques like steganography and custom scripts.
One common trick is altering an image’s metadata or tweaking pixel bits using Least Significant Bit (LSB) encoding, making the hidden code nearly undetectable.
The HP Wolf Security report reveals that attackers use these infected images in phishing scams, GitHub repositories, and even legitimate sites like the Internet Archive.
Once executed, hidden malware can steal data, deploy spyware, and compromise entire networks, affecting individuals, businesses, and even governments.

The bottom line? Not all images are as innocent as they seem. In the wrong hands, they can be digital time bombs. Stay alert.

How Hackers Hide Malicious Code in Images

Hackers are always finding new ways to sneak malware past security systems, and one of their favorite tricks is hiding malicious code inside images. At first glance, these images look completely normal—just a simple JPEG or PNG. But behind the scenes, they can deliver dangerous payloads that infect a victim’s device.

While every attack varies, cybercriminals usually follow a few key steps to embed their threats into images.

1. Choosing the Perfect Image

Hackers carefully select images that won’t raise suspicion. A phishing email, for example, might include an image that looks like a common attachment—perhaps a company logo or an innocent-looking photo. If they’re building a fake website, they might use a banner image or an icon that blends in with the site’s design.

But hackers don’t just pick any image—they get creative. In one case, HP Wolf Security discovered PowerShell code hidden inside an image that, once opened, triggered the download of another malicious file from a seemingly trustworthy website.

Malicious code smuggled inside an image can trigger downloads of more scripts. Source: HP Wolf

This tactic is becoming more common, with cybercriminals using legitimate platforms like The Internet Archive and GitHub to host infected images.

2. Using Steganography to Hide Code

To hide malware in an image, hackers use a technique called steganography. This method allows them to embed malicious code within an image’s data without changing how it looks to the human eye. Specialized steganography tools—many of which are available as open-source software—help attackers achieve this. A skilled hacker can even create their own tools using programming languages like C++ or Java.

3. Encoding Techniques: Metadata vs. Least Significant Bits

There are different ways to hide data in an image, but two of the most common methods are:

Metadata Injection – Hackers embed malicious code within an image’s metadata (the information stored alongside the image, such as its title or description).
Least Significant Bit (LSB) Manipulation – A more advanced method that alters the tiniest, least noticeable bits of the image’s pixel data. Since these small changes don’t affect the image’s appearance, the hidden code remains completely undetectable to the naked eye.

Regardless of the method used, the goal is to make the image appear unchanged while secretly carrying out the hacker’s plans.

4. Connecting the Image to the Hacker’s Network

The image itself isn’t always the main source of infection. Often, it’s just a piece of a larger attack. The code hidden inside the image might:

Download additional malware onto the victim’s device.
Trigger scripts that steal sensitive information (like passwords or banking details).
Redirect the victim to a phishing website.

For example, in a campaign identified by HP Wolf Security, hackers used an infected image to exploit a vulnerability in Microsoft Office (CVE-2017-11882). This flaw allowed attackers to execute harmful scripts, giving them control over the victim’s system. Before launching an attack, hackers test their coded images to ensure they function properly, remain undetectable, and seamlessly connect to their malicious infrastructure.

5. Spreading Malicious Images

Once the infected images are ready, hackers distribute them using various tactics, including:

Phishing emails – Victims receive emails with attachments that appear harmless but contain hidden malware.
Fake software downloads – Hackers disguise malware as popular tools or software cracks, tricking users into downloading infected files.
Social media campaigns – Attackers share malicious images through posts or direct messages, hoping unsuspecting users will click on them.
GitHub and file-sharing sites – Some hackers create fake GitHub repositories that claim to offer useful software, but in reality, they distribute malware.

For instance, one hacker set up a GitHub repository pretending to offer a gaming tool called "spoofer software" (used to bypass security restrictions). In reality, the download contained a dangerous malware known as Lumma Stealer, which could steal sensitive user data.

The Bigger Picture

Cybercriminals are constantly refining their methods, and hiding malware in images is just one of their many tricks. Because these images often blend in with legitimate files, they can easily slip past traditional security measures. This is why advanced detection tools and cautious user behavior are crucial in preventing these hidden threats.

Security experts continue to monitor these evolving tactics, but as hackers grow more sophisticated, the best defense is awareness—knowing the risks and being extra careful before downloading or opening any unexpected image files.

Spoofer software is popular to bypass security controls — but can come with malicious code.

How Do Black Hat Hackers Hide Code in Images?

Cybercriminals are always finding sneaky ways to hide their tracks, and one clever method they use is embedding malicious code inside images. According to the HP Wolf Security Threat Insights Report, it's unlikely that attackers relied on basic image-processing libraries like Pillow or pyexiv2 for their operations. These tools are commonly used in ethical hacking but aren’t designed for stealthy cyberattacks.

Instead, the report points to more specialized tools that hackers likely used:

Steghide – A well-known tool that embeds hidden data inside image files, making it nearly impossible to detect with the naked eye.
OpenStego – A popular open-source steganography tool that allows users to hide information inside images or even other file types.
Custom Scripts – Many hackers write their own scripts in Python, C++, or other programming languages to create more tailored and undetectable ways of hiding data.

In some cases, cybercriminals also leverage generative AI to craft sophisticated attack strategies, such as HTML Smuggling—a technique that sneaks malicious code past security defenses.

A real-world example of this was spotted in April 2024, when security experts at OPSWAT discovered hidden code inside an image used in an HTML Smuggling attack. While hiding code in images and HTML Smuggling aren’t the same, they share similar tactics and goals: bypassing security systems and delivering malware undetected.

As cyber threats continue to evolve, staying aware of these tactics is crucial. It’s a reminder that even an innocent-looking image could be a trojan horse for something much more dangerous.

Smuggling code within HTML is another way to get malicious code onto an unsuspecting client. Source: OPSWAT

How Dangerous Can Malicious Images Be?

Most people see images as harmless—just pictures to be viewed and shared. But in the hands of cybercriminals, images can become powerful weapons. When someone unknowingly downloads, opens, or interacts with a malicious image, hidden code inside it can activate, setting off a chain reaction that could lead to a full-scale security breach.

If the image is designed to install a stealer malware, it silently extracts sensitive information from your device. This could include stored passwords, browser cookies, login credentials, and even financial data like e-wallets and banking details.

If the image is carrying spyware, the situation becomes even worse. The infected device connects to a hacker-controlled server, allowing them to remotely steal any data they want. This could mean screenshots, recordings of private conversations, live video feeds, personal files, or even real-time tracking of everything you type.

The scariest part? These types of malware are designed to stay hidden. Victims often have no idea their system has been compromised—until the damage is already done.

The Bottom Line

Never underestimate the risk of malicious images. What looks like an innocent file can actually be a gateway for hackers to steal data, take over systems, and harm individuals, businesses, and even governments.

Cybercriminals are getting smarter, using images as hidden carriers for malware because it’s a stealthy, effective method that often bypasses security checks. Whether through phishing emails, fake websites, or infected downloads, these attacks are increasing.

The best defense? Be cautious about downloading images from unknown sources. Always verify file origins, keep your security software updated, and think twice before clicking on something that seems even slightly suspicious. In the digital world, a single image can be all it takes for hackers to break in.

FAQs

Are malicious images a type of Zero-Click attack?

No, at least not yet. For now, these infected images can’t harm you unless you interact with them—like opening them using vulnerable software, downloading them, or running them as files. Unlike true zero-click attacks, where hackers can exploit your device without any action on your part, these images still need some level of engagement to be dangerous.

Why do hackers use images to hide malware?

Images, PDFs, and even HTML files make perfect disguises for malicious code. Hackers use them to slip past security systems undetected, trick users into opening them, and spread malware more effectively. Since images seem harmless, people don’t think twice before opening them—making them an ideal vehicle for cyber threats.

How much data can a hacker hide in an image?

That depends on the image size and the steganography technique used. A skilled hacker can embed a surprising amount of hidden data without altering the image’s appearance. The larger and more complex the image, the more information can be secretly tucked inside.