Location privacy protection is an essential but challenging topic in the field of network security. Although the existing research methods, such as k -anonymity, mix zone, and differential privacy, show significant success, they usually neglect the location semantic and the proper trade-off between privacy and utility, which may allow attackers to obtain user privacy information by revealing the semantic correlation between the anonymous region and user's real location, thus causing privacy leakage. To solve this problem, we propose a location privacy protection scheme based on the k-anonymity technique, which provides practical location privacy-preserving through generating an anonymous set. This paper proposes a new location privacy attack strategy termed semantic relativity attack (SRA), which considers the location semantic problem. Correspondingly, a semantic and trade-off aware location privacy protection mechanism (STA-LPPM) is presented to achieve privacy protection with both high-level privacy and utility. To be specific, we model the location privacy protection as a multi-objective optimization problem and propose the Improved Multi-Objective Particle Swarm Optimization (IMOPSO) to generate the optimal anonymous set calculating the well-design fitness functions of the multi-objective optimization problem. In this way, the privacy scheme can provide mobile users with the right balance of privacy protection and service quality. Experiments reveal that our privacy scheme can effectively resist the semantic relativity attack while preventing significant utility degrading.

Objectives: This study aims to evaluate the effect of coronavirus disease 2019 (COVID-19) on the long-term risk of digestive diseases in the general population. Design: Large-scale population-based cohort study based on a prospective cohort. Setting: UK Biobank cohort linked to multiple nationwide electronic health records databases. Participants: The cohort consisted of 112,311 individuals who survived the initial 30 days following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, as well as two control groups: a contemporary group (n = 359,671) without any history of COVID-19, and a historical control group (n = 370,979) that predated the COVID-19 outbreak. Main outcome measures: Main outcomes were predefined digestive diseases. Hazard ratios and corresponding 95% confidence intervals (CI) were computed utilizing the Cox regression models after inverse probability weighting. Results: Compared with the contemporary control group, patients with previous COVID-19 infection had higher risks of digestive diseases, including functional gastrointestinal disorders (hazard ratios [HR] 1.95 (95% CI 1.62 to 2.35)); peptic ulcer disease (HR 1.27 (1.04 to 1.56)); gastroesophageal reflux disease (GERD) (HR 1.46 (1.34 to 1.58)); inflammatory bowel diseases (HR 1.40 (1.02 to 1.90)); gallbladder disease (HR 1.28 (1.13 to 1.46)); severe liver disease (HR 1.46 (1.12 to 1.90)); non-alcoholic liver disease (HR 1.33 (1.15 to 1.55)); and pancreatic disease (HR 1.43 (1.17 to 1.74)). The risks of GERD were stepwise increased with severity of the acute phase of COVID-19 infection. The results were consistent when using the historical cohort as the control group. Conclusions: Our study provides important insights into the association between COVID-19 and the long-term risk of digestive system disorders. COVID-19 patients are at a higher risk of developing gastrointestinal disorders, with stepwise increased risk with the severity and persisting even after one year follow-up.