By Nga Pham
BBC Vietnamese Service
The Vietnamese Communist Party has celebrated its 64th year in power.
A Vietnamese blogger detained by police has said she was freed after promising she would quit writing her blog, which has been critical of the government.
Nguyen Ngoc Nhu Quynh is the last of three bloggers recently detained and then released by police.
A Vietnam Foreign Ministry spokeswoman said the three had been arrested legally for national security reasons.
Analysts say the authorities want to prevent blogs becoming a news source and a tool for opposition groups.
On 27 August, blogger Bui Thanh Hieu, also known as Nguoi Buon Gio, was arrested in Hanoi.
A day later journalist Pham Doan Trang, who worked for one of the most visited semi-official news websites in the country - VietnamNet, was also detained by the security police. She too ran a well-read personal blog.
Blogger Nguyen Ngoc Nhu Quynh was arrested on 2 September in the central city of Nha Trang. All three have now been released.
As official media generally stay silent on any subjects deemed sensitive and controversial by the ruling Communist Party, many Vietnamese have turned to the internet to share information and discuss topics of interest.
Analysts say the communist government fears it can not control the more than two million personal blogs in Vietnam as they become increasingly popular as an information medium.
"The Vietnam Communist Party and its security apparatus cannot tolerate matters they do not control. Territorial surveillance, bloc wardens and informers work when suspects are territorially based," says Vietnam analyst, Carlyle Thayer, from the Australian Defence Force Academy.
"Cyberspace represents a more formidable challenge because anonymous citizens can post their views and exchange ideas with others both inside and outside Vietnam."
Territorial disputes with Beijing over the Paracel and Spratly islands, alongside corruption and religious freedom, are among the most talked about topics.
The Vietnamese government does not want anti-China sentiments to get out of hand, but this is not the only reason for the authorities' concern.
Some people inside the country point out that blogs can also serve as a networking tool for groups with a different agenda from the Communist Party to organise face-to-face meetings.
"Online activities may make the authorities wary, but offline ones are what they're disturbed about," says a Ho Chi Minh City-based journalist who wishes to remain anonymous.
"They cannot control the internet, but they can and will punish whoever wants to act on the ideas they consider reactionary," the journalist says.
In his opinion, the latest developments might be part of the ongoing crackdown on political dissidents that saw dozens interrogated and detained in the last couple of months.
Among them are human rights lawyer Le Cong Dinh, businessman Tran Huynh Duy Thuc and democracy activist Nguyen Tien Trung.