1.
/// <summary>
    /// 过滤不安全的字符串
    /// </summary>
    /// <param name="Str"></param>
    /// <returns></returns>
    public static string FilteSQLStr(string Str)
    {

        Str = Str.Replace("'", "");
        Str = Str.Replace("\"", "");
        Str = Str.Replace("&", "&amp");
        Str = Str.Replace("<", "&lt");
        Str = Str.Replace(">", "&gt");

        Str = Str.Replace("delete", "");
        Str = Str.Replace("update", "");
        Str = Str.Replace("insert", "");

        return Str; 
    }

2.

#region 过滤 Sql 语句字符串中的注入脚本
        /// <summary>
        /// 过滤 Sql 语句字符串中的注入脚本
        /// </summary>
        /// <param name="source">传入的字符串</param>
        /// <returns>过滤后的字符串</returns>
        public static string SqlFilter(string source)
        {
            //单引号替换成两个单引号
            source = source.Replace("'", "''");

            //半角封号替换为全角封号，防止多语句执行
            source = source.Replace(";", "；");

            //半角括号替换为全角括号
            source = source.Replace("(", "（");
            source = source.Replace(")", "）");

            ///////////////要用正则表达式替换，防止字母大小写得情况////////////////////

            //去除执行存储过程的命令关键字
            source = source.Replace("Exec", "");
            source = source.Replace("Execute", "");

            //去除系统存储过程或扩展存储过程关键字
            source = source.Replace("xp_", "x p_");
            source = source.Replace("sp_", "s p_");

            //防止16进制注入
            source = source.Replace("0x", "0 x");

            return source;
        }
        #endregion

3.

/// 过滤SQL字符。
        /// </summary>
        /// <param name="str">要过滤SQL字符的字符串。</param>
        /// <returns>已过滤掉SQL字符的字符串。</returns>
        public static string ReplaceSQLChar(string str)
        {
            if (str == String.Empty)
                return String.Empty; str = str.Replace("'", "‘");
            str = str.Replace(";", "；");
            str = str.Replace(",", ",");
            str = str.Replace("?", "?");
            str = str.Replace("<", "＜");
            str = str.Replace(">", "＞");
            str = str.Replace("(", "(");
            str = str.Replace(")", ")");
            str = str.Replace("@", "＠");
            str = str.Replace("=", "＝");
            str = str.Replace("+", "＋");
            str = str.Replace("*", "＊");
            str = str.Replace("&", "＆");
            str = str.Replace("#", "＃");
            str = str.Replace("%", "％");
            str = str.Replace("$", "￥");

            return str;
        }
4.


/// <summary>
/// 过滤标记
/// </summary>
/// <param name="NoHTML">包括HTML，脚本，数据库关键字，特殊字符的源码 </param>
/// <returns>已经去除标记后的文字</returns>
public string NoHtml(string Htmlstring)
{
    if (Htmlstring == null)
    {
        return "";
    }
    else
    {
        //删除脚本
         Htmlstring = Regex.Replace(Htmlstring, @"<script[^>]*?>.*?</script>", "", RegexOptions.IgnoreCase);
        //删除HTML
        Htmlstring = Regex.Replace(Htmlstring, @"<(.[^>]*)>", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"([\r\n])[\s]+", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"-->", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"<!--.*", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(quot|#34);", "\"", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(amp|#38);", "&", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(lt|#60);", "<", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(gt|#62);", ">", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(nbsp|#160);", " ", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(iexcl|#161);", "\xa1", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(cent|#162);", "\xa2", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(pound|#163);", "\xa3", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&(copy|#169);", "\xa9", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, @"&#(\d+);", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "xp_cmdshell", "", RegexOptions.IgnoreCase);

        //删除与数据库相关的词
         Htmlstring = Regex.Replace(Htmlstring, "select", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "insert", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "delete from", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "count''", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "drop table", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "truncate", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "asc", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "mid", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "char", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "xp_cmdshell", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "exec master", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "net localgroup administrators", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "and", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "net user", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "or", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "net", "", RegexOptions.IgnoreCase);
        //Htmlstring = Regex.Replace(Htmlstring, "*", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "-", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "delete", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "drop", "", RegexOptions.IgnoreCase);
        Htmlstring = Regex.Replace(Htmlstring, "script", "", RegexOptions.IgnoreCase);

        //特殊的字符
         Htmlstring = Htmlstring.Replace("<", "");
        Htmlstring = Htmlstring.Replace(">", "");
        Htmlstring = Htmlstring.Replace("*", "");
        Htmlstring = Htmlstring.Replace("-", "");
        Htmlstring = Htmlstring.Replace("?", "");
        Htmlstring = Htmlstring.Replace("'", "''");
        Htmlstring = Htmlstring.Replace(",", "");
        Htmlstring = Htmlstring.Replace("/", "");
        Htmlstring = Htmlstring.Replace(";", "");
        Htmlstring = Htmlstring.Replace("*/", "");
        Htmlstring = Htmlstring.Replace("\r\n", "");
        Htmlstring = HttpContext.Current.Server.HtmlEncode(Htmlstring).Trim();

        return Htmlstring;
   }
}

5.

public static bool CheckBadWord(string str)
{
string pattern = @"select|insert|delete|from|count\(|drop table|update|truncate|asc\(|mid\(|char\(|xp_cmdshell|exec   master|netlocalgroup administrators|net user|or|and";
if (Regex.IsMatch(str, pattern, RegexOptions.IgnoreCase))
return true;
return false;
}
public static string Filter(string str)
{
string[] pattern ={ "select", "insert", "delete", "from", "count\\(", "drop table", "update", "truncate", "asc\\(", "mid\\(", "char\\(", "xp_cmdshell", "exec   master", "netlocalgroup administrators", "net user", "or", "and" };
for (int i = 0; i < pattern.Length; i++)
{
str = str.Replace(pattern[i].ToString(), "");
}
return str;
}