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In the United States, sensitive health information is protected under the Health Insurance Portability and Accountability Act (HIPAA). This act limits the disclosure of Protected Health Information (PHI) without the patient’s consent or knowledge. However, as medical care becomes web-integrated, many providers have chosen to use third-party web trackers for measurement and marketing purposes. This presents a security concern: third-party JavaScript requested by an online healthcare system can read the website’s contents, and ensuring PHI is not unintentionally or maliciously leaked becomes difficult. In this paper, we investigate health information breaches in online medical records, focusing on 459 online patient portals and 4 telehealth websites. We find 14% of patient portals include Google Analytics, which reveals (at a minimum) the fact that the user visited the health provider website, while 5 portals and 4 telehealth websites con- tained JavaScript-based services disclosing PHI, including medications and lab results, to third parties. The most significant PHI breaches were on behalf of Google and Facebook trackers. In the latter case, an estimated 4.5 million site visitors per month were potentially exposed to leaks of personal information (names, phone numbers) and medical information (test results, medications). We notified healthcare providers of the PHI breaches and found only 15.7% took action to correct leaks. Healthcare operators lacked the technical expertise to identify PHI breaches caused by third-party trackers. After notifying Epic, a healthcare portal vendor, of the PHI leaks, we received a prompt response and observed extensive mitigation across providers, suggesting vendor notification is an effective intervention against PHI disclosures. 

Anycast addressing - assigning the same IP address to multiple, distributed devices - has become a fundamental approach to improving the resilience and performance of Internet services, but its conventional deployment model makes it impossible to infer from the address itself that it is anycast. Existing methods to detect anycast IPv4 prefixes present accuracy challenges stemming from routing and latency dynamics, and efficiency and scalability challenges related to measurement load. We review these challenges and introduce a new technique we call "MAnycast2" that can help overcome them. Our technique uses a distributed measurement platform of anycast vantage points as sources to probe potential anycast destinations. This approach eliminates any sensitivity to latency dynamics, and greatly improves efficiency and scalability. We discuss alternatives to overcome remaining challenges relating to routing dynamics, suggesting a path toward establishing the capability to complete, in under 3 hours, a full census of which IPv4 prefixes in the ISI hitlist are anycast.