What is a .reg file?

About the format

A .reg file is a script for the Windows registry. Double-clicking one doesn't 'open' it — it MERGES it: every key and value listed is written into your registry immediately, and lines whose key starts with a minus sign delete entire keys with no undo. The format is text (modern files are UTF-16 and start with 'Windows Registry Editor Version 5.00'; ancient ones say REGEDIT4), but the data is less readable than it looks: strings are often stored as comma-separated hex bytes, DWORDs are hexadecimal, and expandable or multi-part strings use hex(2) and hex(7) encodings. Tweak guides, IT departments and — inevitably — malware all distribute .reg files, and the dangerous ones target the same handful of locations: autostart Run keys, Image File Execution Options, Winlogon, services and policy keys. The safe workflow is always the same: right-click → Edit to read it (or use a viewer that decodes and risk-flags it), understand every key it touches, and only then merge.

How to open a .reg file

Is a .reg file dangerous?

Potentially, yes. Merging a malicious .reg file can install autostart persistence, disable your antivirus via policy keys, or hijack how programs launch. Read before you merge — always.

Related file types