A Guide to Trojan Horses: Definition, Attack Examples, and Prevention

    Using subterfuge, trojan horse viruses spread malware across devices and networks. Learn what to look for and how to protect your data.

    Trojan Horse Introduction

    The Trojan Horse virus is among the most well-known viruses, taking its name from the mythological wooden horse used by the Greeks to enter the city of Troy and secretly attack their enemies as they slept. The reason for the name is clear since a Trojan Horse virus works in much the same way, concealing its true intent from the user until it is too late.

    However, while businesses and individuals may already be aware of this type of virus, the threat remains thanks to increasing levels of sophistication and a broad range of vehicles used for delivery. So, what is a Trojan Horse virus, and how does it work? Here we explore these questions as well as detail the most common examples of Trojan malware so your organization can stay one step ahead.


    Trojan Horse Virus


    What is a Trojan Horse Virus?

    At its simplest, a Trojan virus is a type of malware that disguises itself as a legitimate download. When the user unsuspectingly downloads the software or document, malicious code hidden within attempts to access sensitive data or gain access systems. It may also try to replicate itself across multiple devices once a single device is connected to the network or internet.

    Often, a Trojan Horse will be disguised as an email attachment or a free-to-download app or file that a user will be relatively familiar with. However, Trojans can also enter a user's system or network through links and ads on social media.

    Once downloaded or installed, the Trojan Horse attack may begin instantly or lie in wait for an opportunity to execute its malicious code. When this happens, the Trojan will attempt to hijack control of systems or upload sensitive data from your device or network to a remote network where it can be used for malicious purposes by cybercriminals.

    How does a Trojan Horse work?

    Much like the Greeks did with the Trojans, a Trojan virus looks to first gain the trust of the user. This can be done in various ways, either by preying on the naivety of less internet-savvy individuals or by slowly building trust through social media or email communication.

    In essence, a Trojan Horse virus spreads through legitimate-looking files, which, when installed on an individual device, may quickly spread to other devices on the network. Once the Trojan Horse is on a computer and multiple devices, it can begin to leverage the malicious code that can attack your systems and networks in many ways.

    A Trojan may replicate itself across a network or download data that can later be leaked or used against the organization. By obtaining access to critical information, cybercriminals can extort or blackmail organizations under the threat of releasing sensitive information to the public.

    What does a Trojan malware attack look like?

    For cybersecurity teams and individual users who suspect a Trojan Horse attack, there are several telltale signs to look out for. Many of these indicators are similar to those you might encounter with other types of malware or virus attacks. However, the first sign users can typically identify is that a document or program does not look or work as it is supposed to once opened.

    However, since there is a variety of different types of malware that may be delivered within a Trojan Horse, it is also important to look for other signs that may include:

    • Slow, unpredictable, or unreliable device performance. This can include mobile devices such as phones or tablets, as well as computers and entire servers.
    • Unsolicited pop-ups, notifications, and even spam interruptions when using your browser or operating system.
    • Unexplained procedures, processes, or programs running from your device. These may be obvious and open simultaneously with other apps or software or go underneath the radar within your operating system.

    Trojan Horse examples

    If a Trojan virus has entered your system, it's crucial to understand how it has gained access and what its ultimate intentions are. This will help you determine how to deal with the specific Trojan Horse and prevent future attacks. Some examples of Trojan Horse attacks include, but are not limited to:

    Backdoor Trojans

    Backdoor Trojan Horse attacks allow remote access and control of your systems. This means that cybercriminals can upload, download, and execute files remotely and at-will to gain access to data or transmit more malicious code to other devices on the network.

    Exploit Trojans

    This type of Trojan Horse looks for weaknesses and vulnerabilities within software, apps, and networks which they can then exploit. Once identified, the Trojan malware enters your device or network through the exploit and injects malicious code.

    Banker Trojans

    As the name suggests, Banker Trojan Horse malware specifically targets information relating to banking and financial transactions made online. This may be achieved using backdoor methods, by spoofing a financial institution's login page or appearing as a legitimate piece of banking software the user accesses.

    Downloader Trojans

    Downloader Trojans wait until a device connects to the internet or network and then installs malware into other systems and devices. By doing this, it can access files and systems across an entire network or spread unopposed from device to device through the internet. Often, they will also connect your systems to remote servers that contain additional instructions on where to find and access files.

    How to prevent Trojan malware

    The first point of contact for cybersecurity teams looking to prevent Trojan Horse attacks is always the user. Ensuring all team members within an organization are well-versed in Trojan Horse types and how they enter devices and systems is a crucial first step.

    This means educating team members on security issues surrounding Trojan Horse malware and ensuring best practices such as:

    • Never download software from untrusted sources
    • Never open attachments from untrusted sources
    • Never run programs from unsolicited or unrecognized emails
    • Ensure all devices have active Trojan antivirus protection

    For cybersecurity teams or individuals, ensuring all operating systems and apps are up to date is also critical, helping to reduce Zero-Day attacks and minimize vulnerabilities across networks. This may also mean regular patch updates for in-house software or other potential vulnerabilities within networks and devices.

    Tracing the source of a Trojan Horse is also essential, as it may expose vulnerabilities in your network, software, and even user behavior. However, since Trojan viruses can enter a network and remain inactive for varying periods of time, this can be challenging for both individuals and cybersecurity teams.

    If Trojan Horse malware is suspected, implementing scanners, antivirus, or malware removal may help to detect and remove the threat from a device or network. In fact, periodic scanning of networks and devices should always be performed by cybersecurity teams to try and identify potential Trojan threats before they can spread or breach security.

    Conclusion: Trojan Horses

    Cybersecurity threats are constantly evolving, so it's important to stay educated about the different types of attacks out there and how to prevent them. Since Trojans can be very difficult to detect and remove once they've infected your system, it's important to be proactive in your defense.

    Ensure all software applications and operating systems are up-to-date, run regular scans, and be careful about the emails you open and attachments you download. If you think you might have a Trojan on your hands, don't hesitate to reach out to a professional for help.

    Learn more about Trojan Horse attack protection from Mimecast, as well as Mimecast’s services for Trojan threat detection and protection.

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