What is Formbook malware?

Formbook's an infostealer that grabs passwords, cookies, screenshots from browsers and apps, then sells the loot underground.

How to spot obfuscated JavaScript in phishing?

Huge file sizes (10MB+), .JS in RAR/ZIP, weird names like cbmjlzan.JS. Scan with VirusTotal first — but don't execute.

Does Windows Defender catch this?

Sometimes, post-decryption. But initial JS often slips through. Enable attack surface reduction rules for PowerShell.

🦠 Ransomware & Malware

10MB JS Time Bomb: How Phishing RARs Unleash Hidden Formbook

Picture this: you unzip a shady RAR from phishing, and boom — a 10MB JavaScript monster rewires your PC for credential theft. Formbook's back, sneakier than ever.

theAIcatchup Apr 10, 2026 3 min read

Deobfuscated JavaScript code from phishing malware dropping Formbook infostealer

⚡ Key Takeaways

Massive 10MB obfuscated JS uses AsmDB for low-level power, evading most AVs. 𝕏
Multi-stage payload: JS persistence → PowerShell AES decrypt/evasion → .NET DLL in MSBuild → Formbook stealer. 𝕏
Unique evolution: JS as full attack platform, predicting more browser-like malware surges. 𝕏

Published by

theAIcatchup

Threat intelligence. Zero noise.

#Formbook #PowerShell loader #obfuscated JavaScript #phishing RAR

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Originally reported by SANS ISC

⚡ Key Takeaways

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