Replace letters and numbers with RANDOM letters and numbers, respectively. Good for obfuscating senstive data before logging.

StringObfuscator.cs

public static class StringExtensions
{
	// Consecutive runs for "Foo Bar 0123456789" generated:
	// xuc iih 3156679205
	// lzr xai 1153091860
	// xxm uoy 5532413549
	public static string Obfuscate(this string input)
	{
		if (input == null) return null;
		var obfuscated = new char[input.Length];
		var random = new Random();
        
		for (var i = 0; i < input.Length; i++)
		{
			if (Char.IsLetter(input[i]))
			{
				obfuscated[i] = (char)random.Next(97, 123);
				continue;
			}
            
			if (Char.IsNumber(input[i]))
			{
				obfuscated[i] = (char)random.Next(48, 58);
				continue;
			}
            
			obfuscated[i] = input[i];
		}
        
		return new String(obfuscated);
	}
}