The government says several Spanish companies have been targeted in ransomware cyberattacks.
The Industry Ministry said Friday the attack affected the Windows operating system of employees' computers, blocking files and demanding a ransom to free up the system.
It said the attacks had not affected the companies' services or data protection of their clients.
Microsoft issued a security update on March 14 about vulnerabilities in the Windows system.
There were no details on which companies were targeted but telecommunications company Telefonica said it had detected a cybersecurity incident that had affected computers of some employees. It said it had activated the necessary measures but gave no further details.
There were no details available on the origin of the attack.
Spain's intelligence agency recommended companies should carry out Windows updates.