System.Net.CookieContainer.ExpireCollection C# (CSharp) Method

        private int ExpireCollection(CookieCollection cc) {
            int oldCount = cc.Count;
            int idx = oldCount-1;

            // minor optimization by caching Now
            DateTime now = DateTime.Now;

            lock (cc) {
                //Cannot use enumerator as we are going to alter collection
                while (idx >= 0) {
                    Cookie cookie = cc[idx];
                    if (cookie.Expires <= now && cookie.Expires != DateTime.MinValue) {

                        cc.RemoveAt(idx);
                    }
                    --idx;
                }
            }
            return oldCount - cc.Count;
        }