This ColdFusion UDF will query the server's request headers to determine if the request is an Ajax form post from jQuery. (jQuery adds a special header to all ajax requests.)

isAjaxRequest.cfm

<cfscript>
function isAjaxRequestPost(){
	var headers = getHttpRequestData().headers;
	return CGI.Request_Method is "POST" and StructKeyExists(headers, "X-Requested-With") AND (headers["X-Requested-With"] EQ "XMLHttpRequest");
}
</cfscript>

<cfif not isAjaxRequestPost()>
	<!--- log attempt, alert admin, etc --->
	<cfheader statuscode="403" statustext="Forbidden">	
	<cfcontent type="text/html; charset=UTF-8"><cfoutput>Forbidden</cfoutput><cfabort>	
</cfif>

<!--- perform database update, modify cookies, upload files, etc --->
<cfcontent type="application/json; charset=UTF-8"><cfoutput>{"status":1}</cfoutput><cfabort>