msvcr71.dll: Microsoft's old C runtime, or a file that only carries the name?

What msvcr71.dll does

msvcr71.dll is the C runtime library of Microsoft's C and C++ compiler version 7.1, the one in Visual Studio .NET 2003. A program built with that compiler calls it for the basic work of the C language: allocating memory, opening and reading files, formatting text, converting numbers and doing maths. The C++ standard library of the same release is msvcp71.dll, and the MFC user interface library is mfc71.dll.

Microsoft's list of Visual C++ Redistributable packages begins with Visual Studio 2005, so there was never a shared package that installs msvcr71.dll for every program. Each program carried its own copy and put it next to its .exe, where Windows looks first. That is why the file is found in many different folders, why Windows does not repair it, and why its name alone says nothing about the file: a genuine copy is identified by where it sits and what it reports about itself.

About .dll files. A .dll file is a library: it cannot run on its own and is loaded into a program's process. It does not appear in Task Manager under its own name; Process Explorer shows which process loaded it.

How to check a copy of msvcr71.dll

Four questions decide it: where the file is, what it says about itself, how big it is, and whether it is signed. A library never shows in Task Manager under its own name, so use these checks instead.

1. List every copy and where it sits. Copies next to the .exe of an old program you installed, in a game's bin folder or in C:\Windows\SysWOW64 are normal. Look closer at copies in Downloads, Desktop, Temp, AppData or ProgramData, and at a copy next to an .exe with a random name.

   Get-ChildItem -Path C:\ -Filter msvcr71.dll -Recurse -ErrorAction SilentlyContinue | Select-Object FullName, Length, LastWriteTime

2. Read the version resource. Microsoft's file reports Microsoft Corporation as the company, Microsoft C Runtime Library as the description and a file version that starts with 7.10. One copy in the public catalogue reports another company and an audio effects description under the msvcr71.dll name: a file like that is not Microsoft's runtime.

   (Get-Item "C:\path\to\msvcr71.dll").VersionInfo | Format-List CompanyName, FileDescription, FileVersion

3. Compare the size. The Microsoft copies in the catalogue are 346,030 or 356,515 bytes. A file far from those sizes is a different file, whatever its version fields say. Use the file check on this page to compare the checksum with the known copies.

   (Get-Item "C:\path\to\msvcr71.dll").Length

4. Check the digital signature. Status Valid with a Microsoft signer means an unmodified Microsoft file. An older build may carry no signature of its own, so NotSigned alone does not prove a fake. HashMismatch or a signer that is not Microsoft does mean the file is not Microsoft's as shipped.

   Get-AuthenticodeSignature "C:\path\to\msvcr71.dll" | Format-List Status, SignerCertificate

5. Find the program it belongs to. Look at the other files in the same folder. A genuine copy sits beside the .exe of a program you can name, often with msvcp71.dll or mfc71.dll. A lone runtime in a folder with no program, or beside a program you never installed, is the reason to keep looking.

A copy that passes these checks clears that one file. It says nothing about the program that brought it: if that program is one you do not recognise, the program is what needs checking.

Do you need msvcr71.dll?

Keep every copy inside an old program you use: without it that program does not start. A copy that failed the checks above came with something else, and the safe way out is to remove that program, not only the DLL.

1. Leave copies in your programs alone. A copy next to the .exe of a program you installed belongs to that program. Deleting it only stops the program from starting, and nothing on Windows puts it back except that program's own installer.
2. Remove old programs you no longer use. Open Settings, Apps, Installed apps, find the program and uninstall it. The program's copy of msvcr71.dll goes with it. A copy in C:\Windows\SysWOW64 left by an older installer can stay: removing it gains nothing.
3. Uninstall a program you do not recognise. If the copy that failed the checks sits beside a program you never installed, uninstall that program from Installed apps. If it has no uninstaller, note the folder path, then delete the whole folder after the scan below, not only the DLL.
4. Run a Microsoft Defender full scan. Open Windows Security, Virus and threat protection, Scan options, Full scan. Quarantine what it finds, then look at Protection history for anything found in Downloads, Temp or AppData.
5. Run the offline scan. Some malware hides while Windows runs. The offline scan restarts the PC and scans before Windows starts. It takes about 15 minutes.

   Start-MpWDOScan

6. Check what starts with Windows. Open Task Manager, Startup apps, and Task Scheduler. After the scan, disable and remove entries that run a program from AppData, ProgramData or Temp that you do not recognise.

Warning signs

Known versions of msvcr71.dll

A public DLL catalogue lists 9 versions of msvcr71.dll, from 1.0.9.813 to 7.10.7031.4, by Microsoft Corporation. Its copies are uploaded by users and not verified, so a checksum match identifies the version, while the digital signature tells you whether the file is genuine. Even a genuine file clears only the file, not the folder: attackers ship genuine libraries next to a program they abuse, so where the copy sits still decides whether it is safe.

Every version with its checksums, and how to fix msvcr71.dll errors on uGetFix

Questions people ask