GPL software on a webserver - "released" or not?

[John Geddes]

I have looke hard, but failed to find any resource that clearly
explains the implications of the GPL for a hosted web service. Can
anyone help?

Simple example: say I wrote a PHP application to work out an
individual's life expectancy, based upon some inputs from the user,
and lots of clever computation - some my own code, but including one
or more GPL-licensed components.

As I understand the GPL, if I only ever use this on my own, local,
PCs, then there is no obligation to release the code to anyone. I
could make money from premium-rate phone calls where the customer told
me their details, I plugged them into the system, and read them back
the answer. The answer might draw on some clever techniques in code
that is subject to the GPL. But because I am selling a service and not
releasing the software, I presume I would be under no obligation to
release the code.

At the other end of the spectrum, if I wanted to distribute the
software for users to run on their own, local, PCs - then the GPL
seems clear: anyone who gets the application must also get the source
code, and be free to distribute it to others on the same terms. (So
whilst I could try to charge $500, the first purchaser could offer it
to others for nothing as long as they included the source code).

But how do I stand if I load the application onto "my" web server
(perhaps I could get an insurance company to pay me for the
application to be accessed via their website as a way of attracting
new customers)?

Does the very act of loading the code onto any webserver constitute
"releasing" the software? (In this case, I would have to release the
code to anyone who asked, whether it was server-side or client-side).

Or is it only the act of transmitting it to a user's PC that is
"releasing"? In this case, would a purely PHP application escape the
need to provide code on the basis that the GPL-licensed PHP is server-
side and is never "released "- only the consequent HTM.

And would the position be different for an application loaded by me
onto a webserver hosting a client's domain but managed by me (ie it
was me doing the uploading so that I never had to "release" the code
to the client)?

John Geddes
England

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Extract from GPL FAQ:
"an organization can [...] use it internally without ever releasing it
outside the organization. But if you release the modified version to
the public in some way ..."