In recent months, though, filtering appears to have been used increasingly as a tool in the ongoing power struggle within Iran's conservative camp.
In the weeks leading up to the March 2 parliamentary elections, which were effectively a competition between conservative factions, a number of websites supportive of President Mahmud Ahmadinejad were reportedly blocked by the country's judiciary, which is closely aligned with Supreme Leader Ayatollah Ali Khamenei.
Several of the filtered websites were said to have posted comments critical of parliamentary speaker Ali Larijani, who is close to Khamenei and a staunch critic of Ahmadinejad.
Mohammad Saeed Zakeri, who edits a pro-Ahmadinejad website, was detained in the preelection crackdown for purportedly writing an article critical of Larijani. His fellow journalist, Meysam Nili Nili, a writer and administrator with the hard-line "Rajanews" website, was reportedly detained in October after Larijani complained about his writing. (Reports say both men have since been released.)
The unusual effort at online censorship has been criticized by a group of hard-line cyberactivists loyal to the clerical establishment.
In an online statement, the cyberactivists said the selective filtering of hard-line content and the detentions were "irrational." And they warned that it could damage the country's "holy" cyberwar.
The activists also argued that some of the websites and blogs that are being filtered played a key role in 2009's postelection crackdown.
"What is the common reason for the blocking of 'Teribon,' 'Serat,' and 'Bibak'? Does the criticism of one of the establishment's top officials deserve such dealing?" they asked.
The managing editor of "Teribon," Mohammad Saleh Meftah, said his website was blocked after it criticized the filtering of other like-minded sites.
"We had posted an article about the increasing cost of criticizing some officials, which subsequently led to the closure of our site," Meftah was quoted as saying in early March.
It's not the first time that the clerical regime's loyalists have voiced disapproval over such selective online censoring.
In 2010, "Rajanews" protested the blocking of a number of hard-line blogs. But it did so even as it appeared to support the continuing censorship of other sites that Iranian authorities deemed immoral or against the country's national interests.
In a move that could signal a further hardening of Iran's tight grip on the Internet, Khamenei on March 7 ordered the creation of a special cybercenter led by top political and military figures.
Ahmadinejad and parliamentary speaker Larijani, as well as the commander of the Islamic Revolutionary Guards Corps and the ministers of telecommunications and culture, are among those who have been appointed to Iran's High Council on Cyberspace.
Iran has also launched a cyberpolice unit and announced that it will launch a national Internet later this spring.
-- Golnaz Esfandiari