Twitter has updated its privacy policy, creating a two-lane service that treats US and non-US users differently. If you live in the US, your account is controlled by San Francisco-based Twitter Inc, but if you're elsewhere in the world (anywhere else) it's handled by Twitter International Company in Dublin, Ireland. The changes also affect Periscope.
What's the significance of this? Twitter Inc is governed by US law, it is obliged to comply with NSA-driven court requests for data. Data stored in Ireland is not subject to the same obligation. Twitter is not alone in using Dublin as a base for non-US operations; Facebook is another company that has adopted the same tactic. The move could also have implications for how advertising is handled in the future.