Australia has halted online collection of national census data after a website where citizens could upload information was subjected to repeated cyberattacks. The Australian Bureau of Statistics said its website had experienced four denial-of-service attacks, in which a torrent of automated requests is sent to overwhelm a site. The last attack, just after 7:30 p.m. on Tuesday, contributed to the overloading of a router, which led to the decision that night to close down online data gathering. The census, which occurs every five years, has been the subject of intense criticism and questions this year over whether the introduction of online data collection could leave Australians’ personal information at risk. Australian officials said on Wednesday that the census system had not been infiltrated and that no data had been compromised.