At least 10 hacking groups using Microsoft software flaw: Researchers

At least 10 different hacking groups are using a recently discovered flaw in Microsoft Corp's mail server software to break in to targets around the world, according to researchers at cybersecurity company ESET.

The breadth of the exploitation adds to the urgency of the warnings being issued by authorities in the United States and Europe about the weaknesses found in Microsoft's Exchange software.

The security holes in the widely used mail and calendaring solution leave the door open to industrial-scale cyber espionage, allowing malicious actors to steal emails virtually at will. Tens of thousands of organizations have already been compromised, Reuters reported last week.

While Microsoft has issued fixes, the sluggish pace of many customers' updates - which experts attribute in part to the complexity of Exchange's architecture - means the field remains at least partially open to hackers of all stripes. Experts are particularly concerned about the prospect of ransom-seeking cybercriminals taking advantage of the flaws because it could lead to widespread disruption.