Anglesey cyber-attack affects island's five secondaries
All five secondary schools on the island of Anglesey have been hit by a cyber-attack.
The council said the attack began on Wednesday.
Officials said affected systems had been disabled to "contain the incident", but warned some personal data could have been compromised, including emails.
The authority's chief executive Annwen Morgan said schools were likely to see disruptions.
Ysgol Syr Thomas Jones, in Amlwch, Ysgol Uwchradd in Bodedern, Ysgol Gyfun Llangefni, Ysgol David Hughes in Menai Bridge, and Holyhead's Ysgol Uwchradd Caergybi are the schools whose systems were known to be affected.
Ms Morgan said: "We discovered the cyber-attack on Wednesday and moved quickly to bring in a team of specialised cyber-technology consultants to investigate. The National Cyber Security Centre will also be providing us with support to resolve matters.
"There is likely to be some disruption at the schools over the coming weeks as systems may need to be restored and others remain offline."
She added: "We are working closely with other partners to support our secondary schools.
"Although we are not currently able to confirm that there has been a data breach, the Information Commissioner's Office has also been made aware of the incident."