The websites of 13 schools were defaced between 3.30pm and 5pm on Wednesday, the Ministry of Education (MOE) said.
This comes just over a week after James Raj Arokiasamy, the alleged hacker who went by the moniker "The Messiah", was charged in court under the Computer Misuse and Cybersecurity Act last Tuesday.
In a statement, the MOE said the ministry is working to restore the sites and the matter has been referred to the police.
Separately, the Singapore Art Museum (SAM) revealed on Wednesday that a file containing personal details had been taken from its website and illegally uploaded onto an overseas server on Nov 5. SAM said it was alerted to this that day by the Infocomm Development Authority (IDA).
The New Paper understands that IDA saw a tweet on Nov 4 from Twitter user CtrlSalad, which said that thousands of e-mail addresses, phone numbers, names and IP addresses were going to be put into the public domain. On Nov 5, the user shared a link to a website where the mailing list had been uploaded.
Within two hours, IDA contacted the server's administrator to take down the file. TNP understands the website is hosted in New Zealand.
DATA FILE REMOVED
SAM has made a police report and removed the data file from its website.
The uploaded document contains about 4,000 names, e-mail addresses and phone numbers from people who took part in SAM's events in 2011 and 2013.
SAM Director Susie Lingham said the museum has contacted the 4,000 people and apologised to them.
She said SAM could not announce this earlier because various agencies needed time to verify the extent of the incident, but it was now necessary to explain what happened because "personal data had been compromised".
Get The New Paper for more stories.