It's not really hard to see why third-party service-based viewers might raise the hackles of Linden Lab (or indeed of some users). When you're using a service-based viewer, your credentials (username and password), activities, inventory and Linden Dollars are exposed to the operator of the viewer.
Additionally, service-based viewers generally cannot pass ethernet MAC addresses as required by Linden Lab's Third Party Viewer policies (some of the supported devices – and particularly mobile devices – simply don't have one).
In any case, your privacy and/or security is tied to the trustworthiness of the viewer operator and all the parties involved with operating the service, any of whom could breach it at a whim.
Nevertheless, a number of service-based viewers are trusted by users, such as AJAX Life – a web-based viewer by UK Wunderkind Katharine Berry – that got its final marching orders from Linden Lab just a few days ago.
Berry's viewer was variously blocked and unblocked from the Second Life grid a number of times before Linden Lab indicated that it was going to pull the plug entirely.
Some (though far from all) of the issues would go away if Linden Lab were to implement one of the standard authentication frameworks, but the newly downsized Lab indicates that resources are too scarce to attempt to do so.
At this moment, it isn't clear if any other service-based viewer operators have also received the thumbs-down, but we would not be surprised. Cloud-based and remote-systems rendering only looks like a safe and secure choice for first-party services. Any other way is a minefield of potential leaks and liability.
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