ASML, the world's largest maker of tools for etching out the powerful microchips at the heart of latest-generation smartphones and computer servers, underpins much of the world's technology infrastructure.
The company did not say when the breach had taken place, but said ASML staff discovered the break-in soon after it occurred.
Many of the world's largest technology companies, with valuable intellectual property, are seen as ripe targets for industrial espionnage, including by foreign governments keen to match those companies' technologies.
"ASML recently discovered unauthorized access to a limited portion of its IT systems," the company said in a statement, adding that it was investigating the intrusion.
"At this time it appears that only a limited amount of data has been accessed. ASML has not found any evidence that valuable files, either from ASML or our customers and suppliers, have been compromised," it added.
On Friday, Dutch technology website tweakers.nl reported that a break-in had taken place and quoted anonymous sources blaming the Chinese government for the attack.
ASML said it could not be certain about the identity of the hackers, adding that it was subject to cybersecurity attacks, "like any other leading organization."
The company said it would provide no further details unless there were significant developments.
© Thomson Reuters 2015