Filtech Hackers launched attacks Tuesday on many Vietnamese websites with the .vn top-level domain, including that of the Dong Nai Customs of the southern province.

It is widely thought to be revenge for Vietnamese hackers stealing the Facebook accounts of many people in the Philippines.

In late July a Philippine hacker had noticed that many Filipino accounts with a large number of followers on Facebook were being sold online in Vietnam.

The same hacker created a post about this on the Facebook group Philippine Cyber Eagles, and showed people how to protect their Facebook accounts from Vietnamese hackers.

Hackers are familiar with the social media platform's errors that they can take advantage of. Thus, they can help users retrieve lost accounts but also hack accounts and sell them for money.

This community has thousands of members in Vietnam, most of them young.

They look out for accounts that are more than 10 years old and have many followers since Facebook offers certain benefits to such accounts.

They then hack them, change the log-in information and sell for a starting price of VND10,000 ($0.43).

These transactions take place openly without Facebook doing anything to stop them.

A Philippine technology journalist with the Facebook name Art Samaniego said Philippine hackers are trying to connect with Vietnamese hackers to resolve this matter.

According to its Ministry of Information and Communications, Vietnam suffered 3,159 cyberattacks in the first six months of this year, a 45.9 percent decrease year-on-year.

Vietnam has more than 64 million Internet users out of a population of 97 million.