Public health officials around the world have agreed that testing and contact tracing are vital to containing the coronavirus pandemic. But for many people, coming forward to get tested — let alone revealing the personal information of friends, family and close associates — is more terrifying than getting Covid-19. In South Korea, where gay marriage is illegal and homophobia is common, officials are struggling to reach thousands of people who may have been exposed to the virus at gay nightclubs in Seoul. In Malaysia, undocumented immigrants and foreign workers say they fear detention or deportation. In India, real and suspected virus patients say they’ve become targets of on- and offline harassment. Governments around the world have released unprecedented amounts of information about actual and potential Covid-19 cases — ages, neighborhoods, travel patterns — all in the name of public health. But it’s also emboldened a new kind of vigilantism and threatened personal privacy, and experts worry harassment and prejudice could undermine the goals of all the disclosure in the first place: containing community spread.