US drugmaker Pfizer and its German partner BioNTech said on Wednesday that documents related to development of their COVID-19 vaccine had been “unlawfully accessed” in a cyberattack on Europe’s medicines regulator.

The European Medicines Agency (EMA), the agency assessing medicines and vaccines for European countries said that it was subjected to cyberattacks. No other details were given.

Pfizer and BioNTech said they did not believe any personal data of trial participants had been compromised and EMA “has assured us that the cyber attack will have no impact on the timeline for its review.”

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No information yet on the attack happened and who are the perpetrators behind it and what information could have been potentially compromised.

The two companies said they had been informed by the EMA “that the agency has been subject to a cyber attack and that some documents relating to the regulatory submission for Pfizer and BioNTech’s COVID-19 vaccine candidate” had been viewed.

Experts said the information that was accessed could be valuable to other countries which are also rushing to develop vaccines.

“When it comes to the data submitted to these kinds of regulatory bodies, we are talking confidential information about the vaccine and its mechanism of action, its efficiency, its risks & known possible side effects and any unique aspects such as handling guidelines,” Marc Rogers, founder of a volunteer group fighting Covid-related breaches, CTI-League told Reuters.

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“It also provides detailed information on other parties involved in the supply and distribution of the vaccine and potentially significantly increases the attack surface for the vaccine,” he added.

A spokeswoman for BioNTech declined further comment. Pfizer did not respond to a request for further comment.