Analysis and Nudging of Personally Identifiable Information in Online Used Markets

In web or mobile app online used markets, users often leave their private contact information intentionally to sell their goods through quick communication. However, the Personally identifiable information (PH) uploaded by users is vulnerable to unwanted advertisement, exploits or even crime. In this work, we examine how PH elements are exposed at popular online used markets in Brazil, China and Korea. Regardless of country, platform, and PH protection system, PH are exposed. From 1-year data collection, we found that phone numbers and email addresses are frequently observed such that 69.43% of posts include phone numbers and 90.86% showed email addresses, and that 36.41% of PII lasted longer than 90 days with the slow PII decay rate of 0.03% per day in Korean used market. To protect the privacy of sellers exposed on the posts, we present a simple nudging web browser extension that detects and notifies PII elements.