.U Subsampled Raw YUV Image .U10 UFile 2010 Tax Return .U11 UFile 2011 Tax Return .U12 UFile 2012 Tax Return .U3D Universal 3D File .U3I U3 Application Information File .U3P U3 Smart Application .U8 3D Lemmings Audio File .UAX Unreal Audio Package .UB Unsigned Byte Audio File .UBJ Universal Binary JSON File .UBOX Universe Sandbox Data File .UC UnrealScript Class .UC2 UltraCompressor 2 Archive .UCCAPILOG Microsoft UCC API Log File .UCE Windows UCE System File .UCF WebEx Media File .UCI UFS Explorer Backup File .UCL Unreal Tournament cache file .UCM Crazy Machines Model File .UCT UC Browser Theme File .UD OmniPage User Dictionary .UDB Dynamics AX User Database File .UDC Adobe InDesign User Dictionary .UDCX Universal Data Connection File .UDEB Debian Package File .UDF Universal Disk Format File .UDK Unreal Engine Map File .UDL Microsoft Universal Data Link File .UDS FIMware database file .UEA Protector Suite QL Encrypted Archive .UFO Ulead File Object .UFR Ultra Fractal File .UFS FreeBSD Unix File System File .UHA UHarc Compressed Archive .UHTML uHTML document file .UI User Interface File .UIBAK UltraISO Backup Disk Image .UIF Universal Image Format Disc Image .UIS WindowBlinds User Interface Specification .UKX Unreal Animation Package .ULAW Raw u-Law Audio File .ULF Universal List File .ULS NetMeeting User Location Service File .ULT UltraTracker Module .ULW u-Law Audio File .ULZ USBlyzer Data Capture File .UMF MediaHolder Universal Media Format File .UML UML Data Object Model .UMLCLASS UML Class Model .UMOD Unreal Tournament Module File .UMS Rune 3D Mesh File .UMX Deus Ex file .UNAUTH SiteMinder Unauthorized Message File .UNI MikMod UniMOD Module .UNITY Unity Scene File .UNITY3D Unity Web Player File .UNITYPACKAGE Unity Package File .UNK UVProbe file .UNKNOWN Unknown File Type .UNL Garmin Unlock File .UNR Unreal Level Map .UNT AutoCAD Unit Definition File .UNX Unix Text File .UOF Uniform Office Document .UOP Uniform Office Presentation .UOS Uniform Office Spreadsheet .UOT Uniform Office Document .UPD Program Update Information .UPDATE ISAPI Update File .UPDATR iConomy Update File .UPF Nokia Phone digital photo file .UPG Firmware upgrade file .UPK Unreal Engine 3 Package .UPOI iGO Points of Interest File .UPR FileMaker user spelling dictionary .UPX Ultimate Packer for eXecutables File .UQM The Ur-Quan Masters Game Data File .URL Internet Shortcut .URR Uniface Signatures File .URT Utah Raster Toolkit File .USA Microsoft Office headers file .USEQ USeq Genome Data File .USER Visual Studio Project User Options File .USERPROFILE Norton Antivirus User Profile File .USERTILE-MS Windows 8 User Tile File .USF Universal Subtitles Format File .USFLIB Nintendo 64 Song Library .USM USM Game Video File .USR FileMaker Pro Database File .UST WiFi SiStr exported user theme file .USTAR Uniform Standard Tape Archive Format File .USX Unreal Static Meshes .UT2 Unreal Tournament Map .UT2MOD Unreal Tournament 2003/2004 Module File .UT3 Unreal Tournament 3 Map File .UT4MOD Unreal Tournament 2004 Module .UT8 Ghost Master Language File .UTC Bioware Creature File .UTF8 Unicode UTF8-Encoded Text Document .UTW Unity Whirld File .UTX Unreal Texture Package .UTXT Unicode Text File .UTZ UIQ Theme Package .UU Uuencoded File .UUD UUDecoded File .UUE Uuencoded File .UVF Uncertain Value Format .UVX Unreal Tournament 2003 Saved Game .UW Unsigned Word Audio File .UWF UltraTracker Wave File .UWL User Word List File .UXX Unreal Tournament Cache .UZIP FreeBSD Compressed Disk Image