Around 1,000 Vietnamese websites were attacked by hackers in the last two days of May, a local hacker forum said Monday.

Among the attacked websites were 15 government-run platforms, with the domain name of .gov.vn, and 50 education (.edu.vn) ones, according to WhiteHat, an online forum for Internet security enthusiasts run by Bkav.

Around 200 websites of the Philippines were also attacked in the same period, between May 30 and 31.

A Chinese hacker group named 1937cn claimed responsibility for the attacks and made them public on their website, according to WhiteHat.

The victimized websites were defaced, or had their interface changed by hackers, via a security loophole found in WebDAV and Fckeditor, software that allows file uploads onto the servers that power these platforms, according to an expert from Bkav, an Internet security firm based in Hanoi.

Bkav said it notified webmasters of the attacked websites shortly after detecting the attacks.

“The method is similar to a mass attack directed at hundreds of Vietnamese websites in 2014,” Ta Duc Thien, head of Web Security with Bkav, said.

The latest attack coincided with the 2015 Asia Security Summit, which kicked off in Singapore on Friday.

China’s illegal island-building in the East Vietnam Sea was one of the key issues discussed by top defense officials from across Asia-Pacific at the event, also known as the Shangri-La Dialogue.

After altering the interfaces of the websites, hackers left messages with content related to the East Vietnam Sea issue, according to WhiteHat.

1937cn was also behind the mass cyberattacks targeting hundreds of Vietnamese websites in May and September last year, tech newswire ICTNews quoted another Bkav representative as saying.

More than 200 Vietnamese websites were compromised between May 4 and 8 by self-proclaimed Chinese hackers, and another 754 ones were hacked on September 2, the country’s Independence Day, according to WhiteHat.

Last year’s attacks also coincided with tensions over an oil rig China illegally stationed in Vietnamese waters in May.

Beijing then withdrew the drilling platform from the waters in July after fierce protests from Hanoi and the international community.

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