PHP is a server side language, it can not search a client pc unless it is running on that machine. This is because php is parsed before the response is sent to the client. Even with a client side script, like javascript, you are religated to only the web accessable folders like cookies and cache. You are pretty much limited to letting the user login and setting a cookie for your site, even this is not fool proof as the client can turn off cookies and you are out of luck. Another solution is to redirect the login page to a secure connection and conduct business from there.
freezea you made me laugh it seems you have copied and paste from here what you have just written at least you answered me thanks!
Bots can be created in PHP, I have created some in the past. What type of bot are you looking for metanek? Check this out, its information on a PHP bot called Alice which is an AI. It has details on other bots too. http://alicebot.blogspot.com/
Learn curl first..just i wanna make bot wont help us to guide you..you need to specific what kinda bot