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What Is a Backdoor & How to Prevent Backdoor Attacks (2021)

Ben Martens Ben Martens What Is a Backdoor & How to Prevent Backdoor Attacks (2021)

A backdoor is any method that allows somebody — hackers, governments, IT people, etc. — to remotely access your device without your permission or knowledge.

Hackers can install a backdoor onto your device by using malware, by exploiting your software vulnerabilities, or even by directly installing a backdoor in your device’s hardware/firmware.

Once hackers log into your machine without your knowledge, they can use backdoors for a variety of reasons, such as:

  • Surveillance.
  • Data theft.
  • Cryptojacking.
  • Sabotage.
  • Malware attack.

Nobody is immune to backdoor hacking, and hackers are constantly inventing new methods and malware files to gain access to user devices.

If you think you’ve been the victim of a backdoor attack, there’s a lot you can do to close the backdoors on your system, assess the damage that’s been done, and prevent another backdoor hack in the future.

What Is a Backdoor & How Does It Work?

What Is a Backdoor & How Does It Work?

In cybersecurity, a backdoor is anything that can allow an outside user into your device without your knowledge or permission. Backdoors can be installed in two different parts of your system:

  • Hardware/firmware. Physical alterations that provide remote access to your device.
  • Software. Malware files that hide their tracks so your operating system doesn’t know that another user is accessing your device.

A backdoor can be installed by software and hardware developers for remote tech support purposes, but in most cases, backdoors are installed either by cybercriminals or intrusive governments to help them gain access to a device, a network, or a software application.

Any malware that provides hackers access to your device can be considered a backdoor — this includes rootkits, trojans, spyware, cryptojackers, keyloggers, worms, and even ransomware.

How Do Backdoor Attacks Work?

What Is a Backdoor & How Does It Work?

In order for cybercriminals to successfully install a backdoor on your device, they first need to gain access to your device, either through physical access, a malware attack, or by exploiting a system vulnerability — here are some of the more common vulnerabilities that hackers target:

  • Open ports.
  • Weak passwords.
  • Out-of-date software.
  • Weak firewalls.

Exploits are targeted attacks that take advantage of software vulnerabilities (usually in web-facing software like browsers, Adobe Flash, Java, etc.) in order to provide hackers access to your system. If you want to know more, you can check out our blog post about zero-day exploits here. For the purposes of this article, all you need to know is that there are malicious websites and ads that scan your computer for software vulnerabilities and use exploits to do things like steal your data, crash your network, or install a backdoor on your device.

So, once a malware file infects your device, or your device is physically compromised (stolen or broken into), or you become the target of an exploit attack, hackers can install a backdoor on your system.

Here are a few examples of the different kinds of backdoors that are frequently used:

  • Trojans. Trojans are malware files that pretend to be legitimate files to gain access to your device. Once you click on the “allow insert-program-here to make changes on your device?” button on your PC, the Trojan is then able to install itself on your device. Trojan backdoors can allow users to access your files and programs, or install more serious malware files on your device.
  • Rootkits. Rootkits are advanced malware threats that are able to hide their activities from an operating system so that the operating system gives security privileges (root access) to the rootkit. Rootkits can allow a hacker to remotely access your device, alter your files, observe your activity, and sabotage your system. Rootkits can take the form of either software or even physically altered computer chips — you can read more about rootkits here.
  • Hardware backdoors. Hardware backdoors are modified computer chips or other firmware/hardware that provide non-users access to a device. This can include phones, IoT devices like thermostats and home security systems, routers, and computers. Hardware backdoors can communicate user data, provide remote access, or be used for surveillance. Hardware backdoors can be shipped with products (either by a rogue manufacturer or for some benign purpose), but they can also be physically installed in the event that a device is stolen.
  • Cryptographic backdoors. Cryptographic backdoors are essentially a “master key” that can unlock every piece of encrypted data that uses a specific encryption protocol. Encryption standards like AES use end-to-end encryption so that only the parties that have exchanged a randomly generated cryptographic key are able to decrypt the information being shared. Backdoors are a way of breaking this secure conversation, manipulating the complex mathematics of a specific cryptographic protocol to give an outside user access to all of the encrypted data being shared between parties.

Examples of Backdoor Attacks

Examples of Backdoor Attacks

  • DoublePulsar cryptojacker. In 2017, security researchers discovered that the DoublePulsar backdoor malware (which was originally developed by the NSA, the US’s National Security Agency) was being used to monitor Windows PCs, installing a cryptojacker on computers with sufficient memory and CPU power. The cryptojacker stole processing power from infected computers to mine Bitcoin, secretly joining thousands of PCs into a massive crypto-mining botnet.
  • Dual_EC (NSA cryptographic backdoor). Dual_EC is a cryptographic protocol that uses a mathematical formula called the elliptic curve to generate complex random numbers necessary to encrypt user data. However, Dual_EC also has a backdoor, meaning it can be decrypted by high-level users with a secret key. The NSA pushed tons of large companies to adopt Dual_EC as their main cryptographic protocol, and in 2013 Edward Snowden leaked documents that proved that the NSA was in possession of the secret keys, essentially enabling them to decrypt and read any communications encrypted with Dual_EC. Companies like Blackberry, RSA, Cisco, and Microsoft all made use of Dual_EC in a variety of their products, which left millions of users open to surveillance by the NSA.
  • PoisonTap. PoisonTap is a backdoor malware that allows hackers to access almost any website that you’ve logged into (including sites that are secured with two-factor authentication). PoisonTap a pretty scary piece of malware, but fortunately, it can only be installed by directly plugging a Raspberry Pi computer into the victim’s USB port. PoisonTap was developed by hacker Samy Kamkar, and it hasn’t been deployed in a widespread attack.

Are You Vulnerable to Backdoor Attacks?

Are You Vulnerable to Backdoor Attacks?

Unfortunately, yes — most users have tons of weak points in their online accounts, networks, devices, and even appliances plugged into the Internet of Things (IoT). Here are some of the methods hackers use to install backdoors onto user devices:

  • Hidden/legitimate backdoors. Hidden backdoors are intentionally installed by software developers to provide remote access for performing legitimate functions such as customer support or resolving software issues. However, most reputable manufacturers only include backdoors with extreme security protections to prevent foul play — but a 2020 report showed that Chinese manufacturer Xiongmai had been shipping thousands of cameras, DVRs, NVRs, and other products with hardware backdoors that could permit anybody (for example, the CCP) to remotely access, operate, and surveill users on their devices.
  • Open network ports. An open port on a network accepts traffic from remote locations, and as a result, it can create a weak point that can be exploited by hackers. Hackers usually target ports that aren’t in use — this allows them to install backdoors that access your device without any of your software alerting you about the intrusion. This shouldn’t be a problem for most home users because our routers’ ports are closed by default. However, tech savvy-users and small business owners need to be very careful about what ports they keep open and what vulnerabilities those open ports create. Many IT professionals use Shodan to keep their networks as secure as possible.
  • Weak passwords. A weak password can give hackers immediate access to your accounts — once hackers have cracked one account, it’s very easy for them to access your other accounts and devices. A good example of how hackers leverage default passwords is the 2016 Mirai botnet that affected 2.5 million IoT devices around the world. Mirai was designed to scan the internet for IoT devices using default passwords, hacking those devices and enslaving them to the botnet simply by entering the proper passwords.
  • Out-of-date software. Hackers use exploit attacks to install malware (including backdoors) on user devices. But if you keep all of your software updated, you’re probably not going to be the victim of an exploit attack.
  • Gullible users. Most malware attacks depend on user error — you want to get a free program or torrent the latest Marvel movie, or you click on a link for a big sale, and then you suddenly end up giving your information away or installing a malware file.

Best Ways to Prevent Backdoor Attacks

Best Ways to Prevent Backdoor Attacks

Backdoors are difficult to detect. Everyday users can’t discover a backdoor just by opening the Task Manager. But there are a few easy steps you can take to keep your device safe from backdoors virus attacks, such as:

Use an Antivirus

Always use advanced antivirus software that can detect and prevent a wide range of malware, including trojans, cryptojackers, spyware, and rootkits. An antivirus will detect backdoor viruses and eliminate them before they can infect your computer. Good antivirus software like Norton 360 also includes tools like Wi-Fi monitoring, an advanced firewall, web protection, and microphone and webcam privacy monitoring to ensure you’re as safe as possible online.

Download with Care

Backdoors are often bundled with seemingly legitimate free software, files, and applications. When downloading any file from the internet, check to see if you’re only getting the file you wanted, or if there are some nasty hitchhikers coming along for the ride. Even a file that behaves like the file you’re looking for could be a trojan. Make sure to always download from official websites, avoid pirate sites, and install an antivirus with real-time protection that can flag malware files before you even download them onto your system.

Use a Firewall

Firewalls are essential for anti-backdoor protection — they monitor all incoming and outgoing traffic on your device. If someone outside of your approved network is trying to get into your device, the firewall will block them out, and if an app on your device is trying to send data out to an unknown network location, the firewall will block that app, too.

Advanced firewalls can detect unauthorized backdoor traffic even when your device’s malware detection has been fooled. Windows and macOS both have pretty decent built-in firewalls, but they’re not good enough. There are a few antivirus programs with good firewalls (McAfee has excellent network protections) and you can also consider purchasing a smart firewall, which is a physical device that you connect to your router to keep your network as safe as possible.

Use a Password Manager

Password managers generate and store login information for all your accounts and even help you log into them automatically. All of this information is securely encrypted using 256-bit AES encryption and locked behind a master password. Advanced password managers like Dashlane can even enhance your password vault’s security using biometric login or 2FA tools like TOTP generators and USB tokens. Because they generate random, complex passwords, password managers make it a lot harder for hackers to get into your network or spread across your network in the event that you get a backdoor installed on your system.

Stay on Top of Security Updates/Patches

Zero-day attacks are pretty rare, and most hackers just recycle the same exploits and malware because it’s cheap and easy for them to do so. Plus, it works. One in three IT professionals (34%) in Europe admitted that their company had been breached as a result of an unpatched vulnerability.

Software developers frequently publish new patches to fix the vulnerabilities in their software, and it’s not hard to install those updates. Many programs even include an auto-update option. If you’re a macOS or Windows user, navigate to your settings and turn “Automatic Updates” on — it’s especially important to keep your OS updated because backdoors depend on fooling your operating system.

What is a backdoor in cybersecurity?

A backdoor is any method that can allow another user to access your device without your knowledge or consent (and usually without the device’s knowledge, either). A backdoor can be installed by software and hardware developers, or it can be installed by cybercriminals in order to gain unauthorized access to a device, install malware, steal user data, or sabotage a network.

How do backdoor attacks work?

In a backdoor attack, hackers first find a weak point or a compromised application in your device to exploit — this could be a vulnerability in an application, an open port on your network, an account with a weak password, or a piece of malware that was installed on your device.

The hacker then uses complex tools to deceive your device, your network, or your online account into thinking that the backdoor is a legitimate application.

Once your device is compromised, the backdoor can be used to deploy malware onto your device (like cryptojackers, rootkits, or ransomware), steal your data and spy on your activity, or just install viruses to crash your device.

What can cybercriminals do with a backdoor?

Depending on how sophisticated a backdoor program is, it can allow hackers to perform malicious activities such as DDoS attacks, sending and receiving files, changing system settings, taking screenshots, and playing tricks like opening and closing the DVD drive.

Hackers can even remotely access your device from their computer using a backdoor, navigating all of your files and software from the safety of their own home.

Edward Snowden revealed that the NSA had forced backdoors into tons of user electronics and even widespread cryptographic protocols, enabling them to listen in on anybody’s conversations, activate microphones and cameras, and gather user data remotely.

How can you prevent backdoor attacks?

There are strategies that can be used to prevent and reduce the risk of a backdoor attack, but the first and most important step in staying safe from malware is getting a reliable antivirus program.

For example, Norton 360 comes with real-time protection (which can prevent backdoor malware from being installed on your computer), a firewall (which can detect and prevent unwanted web traffic), a password manager (which can keep your accounts from getting broken into), a vulnerability scanner (which can tell you if you need software updates), and dark web monitoring (which can warn if your data has been breached).

Aside from that, just use good common sense online. Only use HTTPS websites whenever possible, avoid pirate websites, don’t give your personal information to untrustworthy sites, and scan any files you download with an antivirus program.

About the Author

Ben Martens
Ben Martens
Senior Editor

About the Author

Ben Martens is a cybersecurity journalist with a background in internet ethics, malware testing, and public policy. He resides in Oregon, and when he's not advocating for the rights of internet users, he's walking with his dog and inventing stories with his daughter.