security question...??

hi... a number of you write apache/web/server apps that deal with secure information.. in doing some research it occured to me that a potential weak link is on the client side, regarding the browser? how many of you actually attempt to verify that the browser being used by the client is indeed a legitimate (non-hacked) browser?? or is there even a way to do this? or should i just go back to sleep..?? thanks -bruce bedouglas@earthlink.net