backdoor malware Archives

Tech Optimizer

August 31, 2026

ValleyRAT Backdoor Hides in Signed Adware That Users Add to Antivirus Exclusions

Silver Fox is linked to the distribution of a backdoor malware called ValleyRAT, disguised as the legitimate QN Wallpaper adware application. Once installed, ValleyRAT provides complete control over the compromised machine. The malware uses DLL sideloading to operate under the guise of a legitimate process, bypassing security measures. It disables Windows Defender and adds itself to autorun entries, and can mark its process as critical, causing system crashes if terminated. Kaspersky has identified specific indicators of compromise (IoCs) including hashes, command-and-control servers, and associated domains. In 2026, Kaspersky recorded over 100,000 detections of ValleyRAT affecting more than 1,500 unique users, mainly in China and India.

Tech Optimizer

January 19, 2026

PDFSIDER Malware Actively Used by Threat Actors to Bypass Antivirus and EDR Defenses

PDFSIDER is a sophisticated backdoor malware that bypasses modern endpoint detection and response systems. It is distributed through targeted spear-phishing campaigns that exploit vulnerabilities in legitimate PDF software. The malware is delivered via spear-phishing emails containing ZIP archives with a trojanized executable disguised as the PDF24 App. When executed, it uses DLL side-loading to load a malicious DLL (cryptbase.dll) alongside the legitimate PDF24.exe, allowing attackers to execute code without detection. PDFSIDER establishes encrypted command-and-control channels using the Botan 3.0.0 cryptographic library with AES-256 in GCM mode and operates mainly in memory to minimize detectable artifacts. It collects system information and executes commands through hidden cmd.exe processes. The malware employs advanced techniques to evade detection in sandbox and virtual machine environments, including checks for available RAM and debugger presence. Indicators of compromise include the malicious file cryptbase.dll and various clean files associated with the legitimate PDF24 application. Organizations are advised to enforce strict controls on executable files, provide user awareness training, and monitor DNS queries and encrypted traffic to detect PDFSIDER communications. The malware's behavior aligns with tactics used in state-sponsored espionage rather than financially motivated cybercrime.