A method comprising: generating, by a processing unit, a plurality of requests for a given webpage, each request having at least one unique parameter value of one or more parameters that can affect the response of a web server; sending, by the processing unit, the requests to the web server; receiving, by the processing unit, in response to each request, a corresponding response; and generating, by a processing unit, by analysis of the responses, a list of identifiers of approved scripts to be executed by web-browsers on a plurality of client devices.