How to remove PDFSIDER from infected systems

What kind of malware is PDFSIDER?

PDFSIDER is malware that, once infiltrated, operates as a backdoor. It bypasses security tools by using a fake file that looks legitimate. The technique PDFSIDER uses is called DLL side-loading. Once inside, collects information about the system and allows cybercriminals to run commands remotely. If detected, PDFSIDER should be removed immediately.

More about PDFSIDER

PDFSIDER mostly runs in the computer's memory, which makes it harder for security tools to detect. When it starts, it gives the attacker full remote control to run commands on the system. PDFSIDER achieves this by secretly opening communication channels, running commands through cmd.exe, and making sure no command window appears.

After running the commands, PDFSIDER collects detailed information about the system, creates a unique ID to identify the infected machine, and sends the command results and system data back to threat actors.

Also, PDFSIDER uses strong encryption to secretly send and receive commands. All data is decrypted only in memory and never saved to disk, making it hard to detect. This ensures the attacker's communication stays hidden. Another technique used by PDFSIDER involves checking if it is running on a test device and terminating itself if it detects one to avoid analysis.

With PDFSIDER, cybercriminals can steal sensitive data such as documents, credentials, and system information. Attackers can also monitor the system and use it to spread to other devices. Overall, PDFSIDER is mainly used for espionage and persistent surveillance.

Conclusion

PDFSIDER is a stealthy backdoor designed to evade detection while providing remote control over infected systems. Its memory‑only execution, strong encryption, and environment checks allow it to operate quietly for long periods. These capabilities make it a practical tool for espionage, data theft, and persistent surveillance.

How did PDFSIDER infiltrate my computer?

PDFSIDER is delivered through targeted emails that appear to come from a trusted source and include a ZIP attachment. Inside that ZIP is a file posing as a legitimate installer for a PDF tool called "PDF24 App".

When users run this executable, they do not see any visible program open, but in the background, it triggers the infection because a malicious DLL is placed alongside it and loaded instead of the real system file. This distribution technique is called DLL side‑loading. It is used to bypass security tools and infect the system.

How to avoid installation of malware?

Always keep your operating system and apps up to date. Run regular scans using a trusted antivirus or security program. Only get software from official sites or reliable app stores, and avoid pirated programs, cracks, or keygens. Be careful with unexpected emails or messages, and do not open attachments or click links, especially when they are included in messages from unknown senders.

Additionally, avoid visiting suspicious websites, do not click on pop-ups, ads, or buttons on such pages, and never allow them to send notifications.

If you believe that your computer is already infected, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate infiltrated malware.

Decoy document distributing PDFSIDER (source: resecurity.com):

Instant automatic malware removal:

Manual threat removal might be a lengthy and complicated process that requires advanced IT skills. Combo Cleaner is a professional automatic malware removal tool that is recommended to get rid of malware. Download it by clicking the button below:

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Quick menu:

• What is PDFSIDER?
• STEP 1. Manual removal of PDFSIDER malware.
• STEP 2. Check if your computer is clean.

How to remove malware manually?

Manual malware removal is a complicated task - usually it is best to allow antivirus or anti-malware programs to do this automatically. To remove this malware we recommend using Combo Cleaner Antivirus for Windows.

If you wish to remove malware manually, the first step is to identify the name of the malware that you are trying to remove. Here is an example of a suspicious program running on a user's computer:

If you checked the list of programs running on your computer, for example, using task manager, and identified a program that looks suspicious, you should continue with these steps:

Download a program called Autoruns. This program shows auto-start applications, Registry, and file system locations:

Restart your computer into Safe Mode:

Windows XP and Windows 7 users: Start your computer in Safe Mode. Click Start, click Shut Down, click Restart, click OK. During your computer start process, press the F8 key on your keyboard multiple times until you see the Windows Advanced Option menu, and then select Safe Mode with Networking from the list.

Video showing how to start Windows 7 in "Safe Mode with Networking":

Windows 8 users: Start Windows 8 is Safe Mode with Networking - Go to Windows 8 Start Screen, type Advanced, in the search results select Settings. Click Advanced startup options, in the opened "General PC Settings" window, select Advanced startup.

Click the "Restart now" button. Your computer will now restart into the "Advanced Startup options menu". Click the "Troubleshoot" button, and then click the "Advanced options" button. In the advanced option screen, click "Startup settings".

Click the "Restart" button. Your PC will restart into the Startup Settings screen. Press F5 to boot in Safe Mode with Networking.

Video showing how to start Windows 8 in "Safe Mode with Networking":

Windows 10 users: Click the Windows logo and select the Power icon. In the opened menu click "Restart" while holding "Shift" button on your keyboard. In the "choose an option" window click on the "Troubleshoot", next select "Advanced options".

In the advanced options menu select "Startup Settings" and click on the "Restart" button. In the following window you should click the "F5" button on your keyboard. This will restart your operating system in safe mode with networking.

Video showing how to start Windows 10 in "Safe Mode with Networking":

Extract the downloaded archive and run the Autoruns.exe file.

In the Autoruns application, click "Options" at the top and uncheck "Hide Empty Locations" and "Hide Windows Entries" options. After this procedure, click the "Refresh" icon.

Check the list provided by the Autoruns application and locate the malware file that you want to eliminate.

You should write down its full path and name. Note that some malware hides process names under legitimate Windows process names. At this stage, it is very important to avoid removing system files. After you locate the suspicious program you wish to remove, right click your mouse over its name and choose "Delete".

After removing the malware through the Autoruns application (this ensures that the malware will not run automatically on the next system startup), you should search for the malware name on your computer. Be sure to enable hidden files and folders before proceeding. If you find the filename of the malware, be sure to remove it.

Reboot your computer in normal mode. Following these steps should remove any malware from your computer. Note that manual threat removal requires advanced computer skills. If you do not have these skills, leave malware removal to antivirus and anti-malware programs.

These steps might not work with advanced malware infections. As always it is best to prevent infection than try to remove malware later. To keep your computer safe, install the latest operating system updates and use antivirus software. To be sure your computer is free of malware infections, we recommend scanning it with Combo Cleaner Antivirus for Windows.

Frequently Asked Questions (FAQ)

My computer is infected with PDFSIDER malware, should I format my storage device to get rid of it?

Formatting your storage device will get rid of PDFSIDER, but it is a measure that will also delete all your files. Alternatively, you can use specialized tools like Combo Cleaner, which can remove malware such as PDFSIDER without needing to format your device.

What are the biggest issues that malware can cause?

Malware can be used to steal sensitive information like passwords and financial data, encrypt files, execute other malicious software, grant attackers remote access to a device, mine cryptocurrency, and more.

What is the purpose of PDFSIDER?

PDFSIDER provides attackers with stealthy, long‑term access to infected systems. It acts as a hidden backdoor that enables remote command execution, system monitoring, and data theft while remaining undetected.

How did PDFSIDER infiltrate my computer?

PDFSIDER likely infected your computer after you opened or ran a file that looked legitimate, such as a PDF‑related installer downloaded from an email attachment or a suspicious website. Attackers trick users by packaging the malware inside a ZIP file with a real‑looking program, which loads a malicious DLL in the background using a technique called DLL side‑loading.

Will Combo Cleaner protect me from malware?

Yes, Combo Cleaner can detect and remove most known malware threats. However, advanced malware often hides deep within the system, so performing a full system scan is strongly recommended.