Reuters reports that suspected North Korean hackers have tried to break into the systems of British drugmaker AstraZeneca in recent weeks as the company races to develop its COVID-19 vaccine.

Citing two people with knowledge of the matter, Reuters said the hackers posed as recruiters on networking site LinkedIn and WhatsApp to approach AstraZeneca staff with fake job offers.

They then sent documents purporting to be job descriptions that were laced with malicious code designed to gain access to a victim’s computer.

One of the sources, who spoke on condition of anonymity, said the hacking attempts targeted a “broad set of people” including staff working on COVID-19 research, but are not thought to have been successful.

The sources said the tools and techniques used in the attacks showed they were part of an ongoing hacking campaign that U.S. officials and cybersecurity researchers have attributed to North Korea.

According to Reuters, Microsoft also said this month that it had seen two North Korean hacking groups target vaccine developers in multiple countries, including by “sending messages with fabricated job descriptions.”

South Korean lawmakers also said Friday the country’s intelligence agency had foiled some of those attempts.

In collaboration with the University of Oxford, AstraZeneca has developed a COVID-19 vaccine and is awaiting approval from British regulatory authorities.