Iranian authorities have blocked the use of most "Virtual Private Networks", a tool that many Iranians use to get around an extensive government Internet filter in the country, three months ahead of the presidential election.

A widespread government internet filter prevents Iranians from accessing many sites on the official grounds they are offensive or criminal.

Many Iranians evade the filter through use of VPN software, which provides encrypted links directly to private networks based abroad, and can allow a computer to behave as if it is based in another country.

"Within the last few days illegal VPN ports in the country have been blocked," head of Iran's information and communications technology committee Ramezanali Sobhani-Fard confirmed to Iran's Mehr news agency on 10 March. "Only legal and registered VPNs can from now on be used."

The Iranian government is still allowing citizens to use a short list of approved VPNs which could potentially be more easily monitored for unwanted behavior. Whether Iranians will actually use the government-approved VPNs remains an open question.

Project Ainita, a non-profit championing internet freedom in places like Iran, flagged up the issue at the end of February when access to encrypted international sites using a SSL proxy appeared to be impossible. "Email, proxies and all the secure channels that start with 'https' are not available," a Tehran-based technology expert told Reuters.

About a week and a half after Ainita recommended the public use VPNs to circumnavigate the growing controls, which had already affected millions, it became clear most services were disrupted. This, said Ainita, shows "more signs of the Iranian government trying to block the few remaining ways to circumvent the surveillance and censorship system online… We call on other organisations involved in fighting against internet censorship to join forces with us and think of a solution before it's too late."

Internet users in Iran, like those in China and other nations employing high levels of censorship, are used to using VPNs to get round government filters. Savvy to this, secretary of Iran's Supreme Cyberspace Council Mehdi Akhavan Behabadi announced, via Iranian news agency Mehr (which has brought us such headlines as "US plots finally takes Chavez from Venezuela"), that the government would begin selling access to registered, legal VPNs and start prosecuting anyone using an illegal one. The option wouldn't be available to everyone, but companies that require VPNs for legally acceptable reasons would have to purchase access via the state, meaning the company would become an access-all-areas space for prying government eyes.

According to Reuters, reports also surfaced of internet call providers Skype and Viber being blocked, and the whole affair is looking an awful lot like Iran is stepping up its move from the "untrustworthy" and "unreliable" World Wide Web to a national intranet service. In 2009, around the time of the last presidential election, there was also massive disruption to internet access. Authorities will not want to see a repeat of the Twitter-storm which highlighted a disgruntled sector of Iranian society that time around -- a sector that no longer appeared to be so quiet in the advent of social networking.