(Reuters) - With their paths through the Internet increasingly blocked by government filters, Nooshin and her fellow Iranian opposition-supporters say their information on planned protests now comes in emails.
They say they don't know who sends them.
Internet messages have been circulating about possible rallies on February 11, when Iran marks the 31st anniversary of the Islamic revolution. But the climate in the Islamic Republic is much harder than before last year's post-election protests.
Last June, social media sites were hailed in the West as promising opposition supporters an anonymous rallying ground -- especially when they were accessed via proxy servers that could mask participants' actions and whereabouts.
For determined Iranians now, they are a high-risk tactic in a strategic game with the authorities, amid reports of mounting Internet disruption. Almost 32 percent of Iranians use the Internet and nearly 59 percent have a cellphone subscription, according to 2008 estimates from the International Telecommunications Union.
Since the disputed presidential poll that plunged Iran into its deepest internal turmoil since the 1979 Islamic revolution, the authorities have slowed Internet speeds and shut down opposition websites.
They also boast of an ability to track online action even from behind the proxies.
"This one is also blocked," sighed Nooshin, a student, as she surfed the Web in a cafe in downtown Tehran. "This is more Filternet than Internet."
Speaking in a low voice and wearing a blue Islamic headscarf, the 22-year-old declined to use her real name due to the sensitivity of opposition activism in Iran.
MOMENTUM OF FEAR
The presidential vote was followed by huge protests led by opposition supporters who say the poll was rigged to secure hardline President Mahmoud Ahmadinejad's re-election. The authorities deny that charge.
When their newspapers were shut down after the vote, defeated presidential candidates Mirhossein Mousavi and Mehdi Karoubi launched their own websites. The authorities later blocked them, forcing the opposition to set up new ones.
Much of this action and protest was publicized and tracked on the Internet, especially through micro-blogging site Twitter.
However, concerns are now mounting in Iran that the authorities may be able to track down people who use proxies.
"People are afraid of being identified and are not willing to use them any longer," said Hamid, a shopkeeper in Markaz-e Computre, a popular computer shopping center in north Tehran, speaking on condition of anonymity.
Which is not to say that opposition efforts to plan and publicize their actions have been thwarted.
Afshin, a Web developer who supports the opposition, said the authorities would not succeed: "Whatever the government blocks in the Web, the people find another way," he said.
"It is a cat-and-mouse game which the government cannot win."
Arrayed against the Web activists are the fact that Iran's government is equipped with latest monitoring technology, which enables it to detect computers making a secure connection, said Mikko Hypponen, chief research officer for Helsinki-based F-Secure Corporation.
Some proxy servers use Secure Sockets Layer (SSL) to secure the connection with a remote server. This security layer helps ensure that no other computers can read the traffic exchanged.
When people make these SSL connections -- the same type used in the West for Internet shopping -- the authorities cannot see the content of material accessed. But they could physically raid sites to check on the computers involved.
National police chief Esmail Ahmadi-Moghaddam in January warned Iran's opposition against using text messages and emails to organize fresh street rallies.
"These people should know where they are sending the SMS and email as these systems are under control. They should not think using proxies will prevent their identification," he said.
"If they continue ... those who organize or issue appeals (about opposition protests) have committed a crime worse than those who take to the streets," Ahmadi-Moghaddam added.
Thousands of people were arrested during widespread street unrest after the election. Most have since been freed, but more than 80 people have received jail terms of up to 15 years, including several senior opposition figures.
On January 28, Iranian media said two men sentenced to death in trials that followed the election had been executed. Tension in Iran rose after eight people were killed in clashes with security forces in December, including Mousavi's nephew.
"The security services can turn technology against the logistics of protest," Evgeny Morozov, a commentator on the political implications of the Internet, wrote in the November edition of Prospect magazine, citing experiences in Belarus and elsewhere.
But the authorities are facing determined resistance.
Journalists inside Iran have been banned from attending opposition demonstrations, but that has not kept footage of anti-government gatherings from reaching the Internet.
"It is extremely important for me to check my email messages in order to be informed about the latest developments in the absence of independent free media in the country," said Nooshin, her computer screen repeatedly flashing up the same message in Farsi: "Access to this page is prohibited by the law."
A young customer in the computer shopping center in Tehran said: "It is very important to be unidentified while surfing the Internet these days ... currently the most secure way for us is to have a secure email account."
Hypponen said Iran's international isolation -- especially its tense relationship with the United States -- is likely to hamper its ability to catch Web activists.
"It's easier for an activist from Iran to hide than for a Web criminal," he said. "When chasing criminals, countries help each other."
The United States is also a factor. It cut ties with Iran shortly after its revolution toppled the U.S.-backed Shah, and Tehran and Washington are now at odds over Iran's disputed nuclear work.
Iran has accused the West of waging a "soft" war with the help of opposition and intellectuals inside the country, and officials have portrayed the post-election protests as a foreign-backed bid to undermine the clerical establishment.
In January, U.S. Secretary of State Hillary Clinton challenged Beijing and other governments to end Internet censorship, placing China in the company of Iran, Saudi Arabia and others as leading suppressors of online freedom.
She said "electronic barriers" to parts of the Internet or filtered search engine results contravened the U.N.'s Universal Declaration on Human Rights, which guarantees freedom of information.
Iran's supreme leader Ayatollah Ali Khamenei hit back, accusing the United States of trying to use the Internet as a tool to confront the Islamic Republic.
"The Americans have said that they have allocated a $45 million budget to help them to confront the Islamic Republic of Iran via the Internet," he said in a January 26 speech.
The U.S. Senate voted in July to adopt the Victims of Iranian Censorship Act, which authorises up to $50 million for expanding Farsi language broadcasts, supporting Iranian Internet and countering government efforts to block it.