What Is Oyster?
Oyster, also known as Broomstick, is a rare and advanced type of malware used in highly targeted cyberattacks. Unlike most viruses or spyware, this malware doesn’t leave obvious traces on your computer, as it hides in memory and only becomes active when a specific USB device is plugged in.
Believed to be part of a targeted threat campaign, this APT (advanced persistent threat) malware exhibits advanced anti-forensic and evasion techniques.
First identified by cybersecurity researchers analyzing targeted intrusions against government and defense contractors, Oyster/Broomstick is typically deployed in highly controlled environments, often via spear-phishing, removable media, or compromised trusted update mechanisms.
Oyster Backdoor Summary
| Name | Oyster Backdoor |
| Type | Trojan / Malware Infection |
| Short Description | Aims to steal data from your computer and run different malware actions. |
| Distribution Method | Common infection methods including phishing messages and malware-infected files. |
| Removal Tool |
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Latest Campaigns Delivering Oyster Backdoor
Recent threat intelligence reports have revealed that Oyster is being distributed through a malicious campaign leveraging search engine optimization (SEO) poisoning. In this tactic, attackers manipulate search engine results to rank fake websites that appear to offer legitimate software downloads, such as PuTTY and WinSCP. These sites, however, serve trojanized installers designed to deceive IT professionals and developers searching for trusted tools.
According to research by Arctic Wolf, once a user downloads and runs one of these compromised applications, it silently installs the Oyster/Broomstick backdoor on the system. The malware then establishes persistence by creating a scheduled task that executes every three minutes. This task runs a malicious DLL (twain_96.dll) via rundll32.exe using the DllRegisterServer export function, a technique that leverages DLL registration as a stealthy persistence mechanism.
Oyster Backdoor Malware Technical Characteristics
- Persistence Mechanism: In-memory execution and USB-based reactivation; avoids registry keys or startup folders.
- Command and Control (C2): Uses covert channels and encrypted payloads; activates only under specific conditions.
- Capabilities: File exfiltration, keylogging, clipboard monitoring, system reconnaissance, credential harvesting, USB-triggered behavior.
- Anti-Forensics and Evasion: No files written to disk, no registry changes, masquerades as legitimate processes, triggers only in specific environments.
How to Stay Safe
- Don’t plug in USB drives from unknown or untrusted sources.
- Make sure your organization uses security tools that look for unusual system behavior, not just known threats.
- Unexpected system behavior after inserting a USB, like unusual files appearing or network slowdowns, could be a red flag.
- Organizations should restrict USB access, monitor for strange data transfers, and regularly train staff on cybersecurity awareness.
What to Do In Case of Infection: Removal Steps
Because Oyster is so stealthy, cleaning it requires expert help. IT teams will typically:
- Isolate the affected machine
- Analyze memory for clues
- Reimage the computer (wipe it and start fresh)
- Investigate how the malware got in
N.B. While Oyster is highly sophisticated and may evade most off-the-shelf tools, running a reputable anti-malware/EDR tool is still an essential step, especially for detection of related artifacts, lateral movement, or lesser variants.
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Preparation before removing Oyster Backdoor.
Before starting the actual removal process, we recommend that you do the following preparation steps.
- Make sure you have these instructions always open and in front of your eyes.
- Do a backup of all of your files, even if they could be damaged. You should back up your data with a cloud backup solution and insure your files against any type of loss, even from the most severe threats.
- Be patient as this could take a while.
- Scan for Malware
- Fix Registries
- Remove Virus Files
Step 1: Scan for Oyster Backdoor with SpyHunter Anti-Malware Tool
Step 2: Clean any registries, created by Oyster Backdoor on your computer.
The usually targeted registries of Windows machines are the following:
- HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
- HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
- HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunOnce
- HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce
You can access them by opening the Windows registry editor and deleting any values, created by Oyster Backdoor there. This can happen by following the steps underneath:
Tip: To find a virus-created value, you can right-click on it and click "Modify" to see which file it is set to run. If this is the virus file location, remove the value.Step 3: Find virus files created by Oyster Backdoor on your PC.
1.For Windows 8, 8.1 and 10.
For Newer Windows Operating Systems
1: On your keyboard press + R and write explorer.exe in the Run text box and then click on the Ok button.
2: Click on your PC from the quick access bar. This is usually an icon with a monitor and its name is either “My Computer”, “My PC” or “This PC” or whatever you have named it.
3: Navigate to the search box in the top-right of your PC's screen and type “fileextension:” and after which type the file extension. If you are looking for malicious executables, an example may be "fileextension:exe". After doing that, leave a space and type the file name you believe the malware has created. Here is how it may appear if your file has been found:
N.B. We recommend to wait for the green loading bar in the navigation box to fill up in case the PC is looking for the file and hasn't found it yet.
2.For Windows XP, Vista, and 7.
For Older Windows Operating Systems
In older Windows OS's the conventional approach should be the effective one:
1: Click on the Start Menu icon (usually on your bottom-left) and then choose the Search preference.
2: After the search window appears, choose More Advanced Options from the search assistant box. Another way is by clicking on All Files and Folders.
3: After that type the name of the file you are looking for and click on the Search button. This might take some time after which results will appear. If you have found the malicious file, you may copy or open its location by right-clicking on it.
Now you should be able to discover any file on Windows as long as it is on your hard drive and is not concealed via special software.
Oyster Backdoor FAQ
What Does Oyster Backdoor Trojan Do?
The Oyster Backdoor Trojan is a malicious computer program designed to disrupt, damage, or gain unauthorized access to a computer system. It can be used to steal sensitive data, gain control over a system, or launch other malicious activities.
Can Trojans Steal Passwords?
Yes, Trojans, like Oyster Backdoor, can steal passwords. These malicious programs are designed to gain access to a user's computer, spy on victims and steal sensitive information such as banking details and passwords.
Can Oyster Backdoor Trojan Hide Itself?
Yes, it can. A Trojan can use various techniques to mask itself, including rootkits, encryption, and obfuscation, to hide from security scanners and evade detection.
Can a Trojan be Removed by Factory Reset?
Yes, a Trojan can be removed by factory resetting your device. This is because it will restore the device to its original state, eliminating any malicious software that may have been installed. Bear in mind that there are more sophisticated Trojans that leave backdoors and reinfect even after a factory reset.
Can Oyster Backdoor Trojan Infect WiFi?
Yes, it is possible for a Trojan to infect WiFi networks. When a user connects to the infected network, the Trojan can spread to other connected devices and can access sensitive information on the network.
Can Trojans Be Deleted?
Yes, Trojans can be deleted. This is typically done by running a powerful anti-virus or anti-malware program that is designed to detect and remove malicious files. In some cases, manual deletion of the Trojan may also be necessary.
Can Trojans Steal Files?
Yes, Trojans can steal files if they are installed on a computer. This is done by allowing the malware author or user to gain access to the computer and then steal the files stored on it.
Which Anti-Malware Can Remove Trojans?
Anti-malware programs such as SpyHunter are capable of scanning for and removing Trojans from your computer. It is important to keep your anti-malware up to date and regularly scan your system for any malicious software.
Can Trojans Infect USB?
Yes, Trojans can infect USB devices. USB Trojans typically spread through malicious files downloaded from the internet or shared via email, allowing the hacker to gain access to a user's confidential data.
About the Oyster Backdoor Research
The content we publish on SensorsTechForum.com, this Oyster Backdoor how-to removal guide included, is the outcome of extensive research, hard work and our team’s devotion to help you remove the specific trojan problem.
How did we conduct the research on Oyster Backdoor?
Please note that our research is based on an independent investigation. We are in contact with independent security researchers, thanks to which we receive daily updates on the latest malware definitions, including the various types of trojans (backdoor, downloader, infostealer, ransom, etc.)
Furthermore, the research behind the Oyster Backdoor threat is backed with VirusTotal.
To better understand the threat posed by trojans, please refer to the following articles which provide knowledgeable details.