A DAT file is a container for data that a specific program created and needs to read back later

DAT stands for "data," which is not very helpful — it is the most generic name a file can have. The real meaning depends entirely on which program made it. A DAT file from your email client contains email settings. A DAT file from a video game contains game progress. A DAT file from Windows contains system information. The same three letters can mean completely different things on the same computer.

The reason programs use DAT files instead of more specific names is straightforward: the program already knows what it is looking for. When Outlook creates a file called "Outlook.dat," Outlook does not need the filename to tell it what is inside — Outlook made it, Outlook stored it in Outlook's own folder, and Outlook knows how to read it. The DAT extension is just a way of saying "this is my program's data, not yours."

You will almost never need to open a DAT file yourself. If you try to double-click one, your computer will not know what to do with it, because the file format is private to the program that created it. The file is not broken — it is just not meant for human eyes.

Key Takeaways

  • DAT files are created by specific programs to store their own data, and each program's DAT files are usually unreadable by other programs.
  • You should not delete a DAT file unless you are certain which program created it, because doing so may break that program's settings or saved data.
  • If a program is not working correctly, a corrupted DAT file is sometimes the cause, and deleting and recreating it may fix the problem.
  • Malware sometimes hides inside DAT files, but a DAT file itself is not dangerous — the danger comes from where the file came from.

Where DAT files live on your computer

Most DAT files are stored in hidden folders that you will never see unless you turn on "show hidden files" in your folder settings. Windows keeps system DAT files in places like C:\Windows\System32 or C:\ProgramData. Individual programs store their DAT files in their own process folders, often buried several levels deep.

Some DAT files are temporary — your browser might create one while you are downloading something, then delete it when you close the browser. Others are permanent — a program like iTunes or Thunderbird creates DAT files that stay on your computer for years, holding preferences, cache data, or library information.

The location matters because it tells you whether the DAT file is safe to touch. A DAT file in a program's own folder is almost certainly meant to be there. A DAT file sitting on your desktop or in your Downloads folder is more suspicious, because programs do not normally put their data there.

When a DAT file causes problems

A DAT file can become corrupted if the program that created it crashes while writing to the file, or if your computer loses power suddenly. When this happens, the program may refuse to start, or it may start but lose all its settings. You might see an error message that mentions the filename, or you might just notice that the program behaves strangely.

If you suspect a corrupted DAT file, the first step is to close the program completely and restart your computer. This clears the file from memory and gives the program a fresh chance to read it. If the problem persists, you can try deleting the DAT file — most programs will create a new one with default settings the next time they start. You will lose any customizations you made, but the program will work again.

Before you delete anything, write down the full path and filename. If deleting the file does not help, you can restore it from a backup or from your Recycle Bin. Never delete a system DAT file (one in Windows\System32) unless you are following specific instructions from Microsoft or a trusted tech support person.

DAT files and security

A DAT file is just a container — it is not inherently dangerous. However, malware can hide inside a DAT file the same way it can hide inside any other file. The risk comes from where the file came from, not from the DAT extension itself.

If you downloaded a DAT file from the internet, especially from an untrusted source, run it through a virus scanner before opening it or moving it to a program folder. If a program you installed created unexpected DAT files in unusual locations, that is a sign something went wrong during installation — uninstall the program and scan your computer.

The safest rule is straightforward: do not manually open DAT files. Let the programs that created them handle them. If you find a DAT file you did not recognize, search the filename online to learn which program created it. If you cannot identify it and you did not install the program yourself, delete it.

Common DAT files you might see

Windows creates several DAT files for its own use. The file "Thumbs.db" (technically a database, not a pure DAT file) stores thumbnail previews of images in folders. The file "desktop.ini" holds folder display settings. These are harmless and should be left alone.

Email programs like Outlook and Thunderbird create DAT files to store message data, contact information, and account settings. Video games create DAT files to hold game progress, graphics, and audio. Media players like iTunes create DAT files for library data and playback history. Antivirus software creates DAT files to store virus definitions and scan logs.

If you see a DAT file and want to know what it is, open the folder it is in and look at the program name. If the folder is called "Outlook" or "Thunderbird" or "iTunes," you have your answer. If the folder name does not match any program you recognize, search the filename online — someone else has probably encountered it and documented what it does.

How to find and manage DAT files safely

To see hidden DAT files on Windows, open File Explorer, click the View tab, and check the box for "Hidden items." On a Mac, open Finder, press Command+Shift+Period, and hidden files will appear. Once you can see them, navigate to the program folder you are interested in and look for DAT files.

If you want to back up a program's settings before deleting a DAT file, copy the entire folder containing the DAT file to an external drive or cloud storage. This way, if something goes wrong, you can restore the original. Most programs will not complain if you restore an old DAT file — they will just use the old settings.

Never delete a DAT file from a system folder unless you are certain you know what it does. If a program is misbehaving and you think a DAT file is the cause, try restarting first, then uninstalling and reinstalling the program. This is safer than manually deleting files, because the installer will set everything up correctly.

Frequently Asked Questions

Can I delete a DAT file without breaking anything?

It depends on which DAT file. If it is in a program's own folder and the program is not currently running, you can usually delete it safely — the program will create a new one with default settings when it starts. If it is in a Windows system folder, do not delete it unless you are following specific instructions. When in doubt, back up the file first.

Why does my antivirus flag a DAT file as suspicious?

Antivirus software sometimes flags DAT files because malware can hide inside them. This does not mean the file is definitely infected — it means the scanner found something that looks like malware code. If the file is in a program folder you installed yourself, it is probably safe. If you downloaded it from the internet, scan it again with a different antivirus tool to be sure.

What should I do if a program keeps creating new DAT files?

This is usually normal — programs create DAT files as they run and update them when you change settings. If a program is creating thousands of DAT files or creating them in unusual locations, uninstall it and reinstall it fresh. If the problem continues, the program may be corrupted or malicious.

Can I convert a DAT file to a format I can read?

Not reliably, because you do not know the internal structure of the file. Some DAT files are actually just renamed versions of common formats (like a DAT file that is really a JPEG image), but most are proprietary. Your best option is to use the program that created the file — it knows how to read and export the data inside.

Is it safe to move a DAT file to a different folder?

No. Programs expect their DAT files to be in specific locations. If you move a DAT file, the program will not find it and will create a new one, leaving the old one orphaned. If you need to back up a DAT file, copy it instead of moving it, and keep the copy in a separate location like an external drive.