SquirrelMail and PHP

[Kh Linux]

Dear All:

I hope, there is a PHP guru here to help me.

When I was testing SquirrelMail last night, I found that, I could no longer
press the 'BACK' button on the browser after I signed out.

I've always wanted to do this on some of my PHP applications but do not know
how.

Could someone please tell me how that is done in PHP, or point me to a good
site for this? Sorry, I more PHP-related; but i thought this list could be
of help.

Thanks,
Vidol