Simple password generator

PasswordGenerator.cs

using System;
using System.Text;

namespace Common.Utility
{
    public class PasswordGenerator
    {
        public static string Create(int length = 8)
        {
            const string valid = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
            var res = new StringBuilder();
            var rnd = new Random();
            while (0 < length--)
            {
                res.Append(valid[rnd.Next(valid.Length)]);
            }
            return res.ToString();
        }
    }
}