Agree with Mark. Prevent the SQL injection attacks. Check these
SQL injection
SQL Injection Attacks and Some Tips on How to Prevent Them[
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SQL injection attacks[
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SQL Injection Knowhow[
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SQL Injection and Cross-Site Scripting[
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For redirection & messagebox, see this
ClientScript.RegisterStartupScript(Page.GetType(), "Message", "alert('Successful Registered');window.location='login.aspx';", true);
If AJAX used in page,
ScriptManager.RegisterStartupScript(Page, Page.GetType(), "Message", "alert('Successful Registered');window.location='login.aspx';", true);