Hundreds of organizations in the U.K. have been impacted by a security breach at accounting software giant Sage over the weekend. 

According to a post on Sage’s website, it says that unauthorized access using an internal login has impacted a “small number” of its U.K. customers. It is currently working with authorities to investigate the situation.

“Our customers are always our first priority so we are communicating directly with those who may be affected and giving guidance on measures they can take to protect their security,” Sage said in a statement. Sage has set up a helpline to assist impacted customers.

Nearly one-quarter of all data breaches are still caused by compromised credentials, according to recent research by the Cloud Security Alliance.