Ang Mo Kio Town Council's website was hacked on Monday - the second People's Action Party-linked website to be compromised in less than two weeks.
The hacker who got into pre-school operator PAP Community Foundation's (PCF) website on Oct 17 is believed to be behind the latest case, having again signed off as "The Messiah".
Police confirmed they are investigating both cases, the earlier of which saw "The Messiah" post a message demanding a "proper investigation" into an incident at one of PCF's centres, where a baby was allegedly scalded by hot coffee.
Ang Mo Kio GRC MP Ang Hin Kee told The Straits Times that as the town council's website carried only public information, no personal data had been compromised: "We need to be vigilant. Hacking can happen any time and anywhere. Each time we try to step up the level of security, it's not the end."
Technology experts said the hackings should serve as a warning that some sites are not as secure as they should be - a point the hacker made with his post on the town council site.
On Sunday, the website of sneaker brand Converse Singapore was also hacked. Last month, City Harvest Church co-founder and singer Ho Yeow Sun's website was defaced by "The Messiah".
As the hacking targeted mostly content-based websites and "not exactly high-profile ones", Professor Ang Peng Hwa, director at the Singapore Internet Research Centre, doubted it was part of "something more sinister".
Mr Terrence Tang, senior director of consumer business at security firm Trend Micro, felt the hacker who posted messages on both PAP-linked websites probably wanted to share his opinions, "even though it wasn't the best way to do it".