Malicious and Low Credibility URLs on Twitter During the AstraZeneca COVID-19 Vaccine Development.

We investigate the link sharing behavior of Twitter users following the temporary halt of AstraZeneca COVID-19 vaccine development in September 2020. During this period, we show the presence of malicious and low credibility information sources shared on Twitter messages in multiple languages. The malicious URLs, often in shortened forms, are increasingly hosted in content delivery networks and shared cloud hosting infrastructures not only to improve reach but also to avoid being detected and blocked. There are potential signs of coordination to promote both malicious and low credibility URLs on Twitter. Our findings suggest the need to develop a system that monitors the low-quality URLs shared in times of crisis.