Carrie brings up a good point that should be addressed.
If I hire BCSE, WebsiteCM, Paul D or anyone else to do a MOD, security check, upgrade or anything else and they ask to put something like that in my site where it is not visible to my customers I have no problem with it at all. They have provided me with a service and the monetary amount only partially covers their work. I would of course want to know where it is so that if anything happened like with PHP I could pull it out. (Although I doubt I would have to ever worry about the three I mentioned)
On the other hand putting something like that on someones website without disclosure is in my book unethical.
Mike