Hackers broke into the website of Brazil's statistics agency on Friday, the latest in a series of attacks on the South American nation's government sites.

The incident comes in the midst of a wave of high-profile Internet attacks on targets ranging from U.S.-based banking group Citigroup Inc to the U.S. Senate that have spurred global concerns about cyber security.

Brazil's statistics agency, known as IBGE, took its website offline for close to five hours following the attack, in which hackers replaced the opening page of the site with a notice with a human eye in the colors of the Brazilian flag.

IBGE said the hackers did not gain access to its research databases.

This month, the government will see the biggest number of virtual attacks in its history by Fail Shell. These attacks are as a protest by a nationalist group that wants to make Brazil better, the notice read. The note was signed FIREH4CK3R.

Several Brazilian government sites have been attacked this week, including the presidency, the sports ministry and the tax collection agency.

Brazil's culture ministry said on Friday it blocked what appeared to a hacker attempt to take down its site.

Advisors for the president of Brazil's Chamber of Deputies, Marco Maia, said his Twitter account was briefly hacked.

Separately, the hacking group known as LulzSecBrazil, linked to the Lulz Security group of hackers, on Thursday released via Twitter what it called personal data on President Dilma Rousseff and Sao Paulo Mayor Gilberto Kassab.

LulzSecBrazil also released personal information including identification numbers and bank details of employees of state-controlled oil company Petrobras, the Folha de S. Paulo newspaper reported on its website on Friday.

The group had taken that information from Petrobras computers, Folha said.

Petrobras in a statement denied that the information referenced by Folha had been obtained by hackers, adding that it was investigating the source of the information.

There was no breach of the internal network or of the company's site, Petrobras said.

The IBGE hackers took a shot at LulzSec, saying on the site's replaced opening page: There's no room for groups without an ideology such as LulzSec or Anonymous in Brazil.

LulzSec has made widely publicized assaults on Sony Corp, the U.S. Central Intelligence Agency, News Corp's Fox TV and other targets. The attacks have mostly resulted in temporary disruptions to websites and the release of user credentials.

LulzSec said on Monday in a Twitter message that it was seeking to hack government websites to leak classified government information.

(Reporting by Maria Pia Palermo and Brian Ellsworth; writing by Luciana Lopez and Brian Ellsworth; editing by Anthony Boadle)