| .MACHACHA | Pescados Software | Varmuuskopiointitiedostot | Split Control File | MacHacha | Pescados Software |
| .MBF | Microsoft Corporation | Varmuuskopiointitiedostot | Microsoft Money Backup File | Microsoft Money | Microsoft Corporation |
| .MBK | dBase, LLC | Varmuuskopiointitiedostot | dBASE IV Multiple Index Backup File | dBase | dBase, LLC |
| .MBU | Sony | Varmuuskopiointitiedostot | Sony CAV-M1000ES Memory Backup File | Sony CAV-M1000ES | Sony |
| .MBW | Firesage Solutions | Varmuuskopiointitiedostot | MBRWizard Archive | Firesage Solutions MBRWizard | Firesage Solutions |
| .MBZ | Unknown Developer | Varmuuskopiointitiedostot | Pogoshell NES Emulator Plugin | PogoShell | Unknown Developer |
| .MDBACKUP | Apple | Varmuuskopiointitiedostot | iPhone Data Backup File | Microsoft Notepad | Microsoft Corporation |
| .MDO | Alcohol Soft | Varmuuskopiointitiedostot | Alcohol 120% Split Image File | Alcohol 120% | Alcohol Soft |
| .MEM | Microsoft Corporation | Varmuuskopiointitiedostot | FoxPro Variable File | Microsoft Visual FoxPro | Microsoft Corporation |
| .MIB | Milenix Software Ltd. | Varmuuskopiointitiedostot | MyInfo Topic Backup | MyInfo | Milenix Software Ltd. |
| .MIG | Microsoft Corporation | Varmuuskopiointitiedostot | Windows Migration Backup File | Windows Easy Transfer | Microsoft Corporation |
| .MKZ | Interscape | Varmuuskopiointitiedostot | PokerOffice Database Backup File | PokerOffice | Interscape |
| .MON | Mozilla | Varmuuskopiointitiedostot | Firefox Monday Bookmark Backup File | Mozilla Firefox | Mozilla |
| .MPB | FJ Soft | Varmuuskopiointitiedostot | MyPhoneExplorer Backup File | MyPhoneExplorer | FJ Soft |
| .MPR | Open Source | Varmuuskopiointitiedostot | Bibexcel Data | BibExcel | Open Source |
| .MRBAK | Paramount Software UK Ltd | Varmuuskopiointitiedostot | Macrium Reflect Backup File | Macrium Reflect | Paramount Software UK Ltd |
| .MS_ | Microsoft Corporation | Varmuuskopiointitiedostot | Microsoft Windows WinHelp Compressed Data | Microsoft Windows | Microsoft Corporation |
| .MTB | Digistore Solutions | Varmuuskopiointitiedostot | MediaTracker Database Backup File | MediaTracker | Digistore Solutions |
| .MYC | Joshua Cannon Butcher | Varmuuskopiointitiedostot | Simply Safe Backup Archive | Simply Safe Backup | Joshua Cannon Butcher |
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