Dangerous File Extensions
Before you click on an email attachment, check its file extension (the letters after the dot). Use this database to see if it is safe or a known malware vector.
| Extension | Type | Danger Level | Description |
|---|---|---|---|
| .exe | Executable | Critical Risk | A direct Windows program. Never open this from an email. |
| .scr | Screensaver | Critical Risk | Actually a hidden executable file. Heavily used by older malware. |
| .bat | Batch File | Critical Risk | A script that runs commands directly on your computer. |
| .vbs | VBScript | Critical Risk | A script that executes code via Windows Script Host. |
| .js | JavaScript | Critical Risk | While normally safe inside a browser, downloading and running a raw .js file will execute it directly on your computer. |
| .docm | Macro Document | High Risk | A Word document that contains embedded code (macros). Often used in spear-phishing. |
| .xlsm | Macro Spreadsheet | High Risk | An Excel spreadsheet with embedded macros. Frequently used to distribute ransomware. |
| .zip | Compressed Archive | Medium Risk | Safe on its own, but hackers use zip files to bypass email scanners and hide the real malware inside. |
| .iso | Disk Image | Medium Risk | Acts like a virtual CD-ROM. Recently abused by hackers to bypass Windows security warnings (Mark-of-the-Web). |
PDF Document | Low Risk | Generally safe to view. The main risk is phishing links hidden inside the text. | |
| .txt | Plain Text | Generally Safe | Cannot execute code. (However, always ensure the file doesn't end in .txt.exe!) |
| .jpg | Image | Generally Safe | Standard image file. (Make sure you have file extensions visible in Windows so a hacker can't trick you with image.jpg.exe) |
The "Hidden Extension" Trick
By default, Windows hides file extensions for "known file types" to make things look cleaner. Hackers absolutely love this feature.
If a hacker names their virus invoice.pdf.exe, Windows will hide the .exe part. To you, it looks exactly like a harmless file named invoice.pdf. When you double-click it expecting a document, it runs the virus instead.
How to show File Extensions in Windows:
- Open File Explorer (Press the Windows Key + E).
- Click the View tab at the top.
- Check the box next to File name extensions.