How can you securely delete a file (overwrite before delete)?

Question

ICSM Computer · Answer

To securely delete a file in C#, you should overwrite its content with random or zeroed data
before deleting it. This prevents file recovery tools from retrieving the original content from disk.
Step-by-Step: Secure File Deletion
Overwrite the file contentFlush to diskDelete the file
Example: Overwrite with Random Data, Then Delete
using System;
using System.IO;
using System.Security.Cryptography;
public static class SecureFileDelete
{
    public static void SecureDelete(string filePath, int overwritePasses = 1)
    {
        if (!File.Exists(filePath))
            return;
        FileInfo fileInfo = new FileInfo(filePath);
        long fileLength = fileInfo.Length;
        using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Write))
        {
            byte[] buffer = new byte[4096];
            RandomNumberGenerator rng = RandomNumberGenerator.Create();
            for (int pass = 0; pass andlt; overwritePasses; pass++)
            {
                fs.Position = 0;
                long totalWritten = 0;
                while (totalWritten andlt; fileLength)
                {
                    rng.GetBytes(buffer);
                    int bytesToWrite = (int)Math.Min(buffer.Length, fileLength - totalWritten);
                    fs.Write(buffer, 0, bytesToWrite);
                    totalWritten += bytesToWrite;
                }
                fs.Flush(true); // flush to disk
            }
        }
        // Optionally truncate and delete
        File.Delete(filePath);
    }
}
Parameters
overwritePasses: Number of times to overwrite the file (1 is usually enough; 3 for higher security).Uses RandomNumberGenerator instead of Random for cryptographic quality.
Notes
This works best on traditional hard drives.On SSDs, the OS and drive firmware may ignore overwrite attempts due to wear leveling and deferred writes —
use full-disk encryption or OS-level secure delete for SSDs.Truncating the file to zero bytes after overwrite is optional, but often unnecessary.

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How can you securely delete a file (overwrite before delete)?

ICSM Computer

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Step-by-Step: Secure File Deletion

Example: Overwrite with Random Data, Then Delete

Parameters

Notes

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