State-backed hackers from North Korea and Russia have been targeting organisations working on a coronavirus vaccine, Microsoft has said.
It said a Russian group nicknamed "Fancy Bear" and North Korean groups dubbed "Zinc" and "Cerium" were implicated in recent cyber-attacks.
The UK's National Cyber Security Centre (NCSC) has previously said Russian hackers were targeting vaccine research.
But Russia denied it was responsible.
Microsoft, which develops cyber-security software, said it had detected attempts to break into the computer systems of seven pharmaceutical companies.
Vaccine researchers in Canada, France, India, South Korea, and the United States were also targeted.
Microsoft said the Russian group had used "brute force" tactics, trying to log in to accounts using millions of different passwords.
One of the North Korean groups sent emails posing as World Health Organization officials and tried to trick people into handing over their login credentials.
Some of the break-in attempts failed, but Microsoft warned that some of them had been successful.
Russia has previously denied targeting vaccine research. The Russian embassy in Washington, USA told news agency Reuters it had nothing further to add.
North Korea's representative to the United Nations has not yet responded to messages seeking comment.
In a blog post, Microsoft called on world leaders to "affirm that international law protects health care facilities and to take action to enforce the law".
This is not the first time that states have been accused of targeting vaccine work.
In July, the UK said Russian intelligence was behind the targeting of UK research, including the Oxford vaccine.
The US also accused China of similar activity.
Both countries have denied it.
All of this is part of a global race for a vaccine as countries seek advantage over each other.
There are enormous economic, social and health benefits - as well as prestige abroad and legitimacy at home - in developing treatments and vaccines first and fast.
Most of the state-based campaigns have been about espionage - stealing information - rather than disruption but there have also been a growing number of cases of criminal groups using ransomware against hospitals.
Microsoft has urged governments around the world not to target healthcare.