To add to the confusion, there are multiple versions of GPL.
GPL can be used in proprietary software. Just add Google. It only requires you open up your changes to the code if you distribute your product. So if you use GPL for a webservice, you’re covered.
Well that is if you use GPL v1 or v2.
Early drafts of GPL v3 attempt to revert this by requiring give back when code is “released” as a web service. This is controversial and I don’t know if they’ll keep it or not.