Welcome to the Lounge

private static Random rnd;

// 'source is not altered
public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source)
{
    rnd = new Random((Int32)DateTime.Now.Ticks);

    List<T> slist = source.ToList();

    int scount = slist.Count();

    int ndx;

    while (--scount >= 0)
    {
        ndx = rnd.Next(0, scount);

        yield return slist[ndx];

        // error
        slist[ndx] = slist[scount - 1];

        // no error
        // slist[ndx] = slist[scount];
    }     
}

Dan Neely wrote:

If you're seeding off of a time, you've got a much more serious problem than just a low number of bits of entropy. You're using a predictable seed which means an attacker can guess it relatively easily and pwn you much faster than brute force.

Jacquers wrote:

It works, but you don't necessarily understand the solution.

OriginalGriff wrote:

I do not understand the "grab random code from the internet and hope it works" mentality - it just seems counterproductive in the long term to me.