CAIRO – President Hosni Mubarak's supporters took their battle against anti-government protesters to cyberspace but their voices were drowned out by an army of tech-savvy activists willing to wage keyboard war.

Anti-regime street protests had for years been stifled by Egypt's powerful security apparatus but, much to everyone's surprise, it only took a few clicks to launch the biggest ever challenge to Mubarak's 30-year presidency.

After a groundbreaking uprising in Tunisia last month forced president Zine El Abidine Ben Ali to flee after 23 years in power, Egyptian activists quickly mobilised pro-democracy protests through Facebook pages and Twitter messages.

On Tuesday, the protests were energised by the release of 30-year-old Google marketing executive and formerly anonymous founder of one of the online protest sites, Wael Ghonim, after 12 days in detention.

But the educated and technically skilled activists were faced with a brief, yet fierce, challenge by Mubarak supporters.

Facebook pages calling for the protests -- including by the pro-democracy April 6 Movement and Khaled Said Facebook page -- were flooded with angry posts condemning the anti-regime demonstrations.

The new wave of pro-regime posts accused the cyber-rebels of being foreign spies, agents or merely unpatriotic.

"You who support April 6 and Khaled Said, I'm sure you are supported by Zionists, or Hamas or Hezbollah," Ahmed Shekoo wrote on the Khaled Said page, named after an Egyptian man who died after a police beating in Alexandria.

Mubarak supporters used aggression, expletives, scare tactics or emotional appeals to get their message across.

"I can't believe what you're doing to the man, after all the president is the symbol of Egypt, and he served the country for 30 years," said one woman.

Another calling herself "Ana Nana" even invited Mubarak to seek refuge in her "modest home", and others branded protesters "sons of whores trying to destabilise the country".

The intensity of the online battles seemed to mirror the fierceness of battles waged on the streets, leading some activists to believe they were targeted as part of an organised government campaign.

Wednesday and Thursday last week saw bloody clashes in Cairo between supporters and foes of the 82-year-old president that left 11 people dead and scores more injured.

"There were so many online comments denouncing the demonstrators, so many insults, but after Friday, they decreased," said Salah Mohammed, a protester affiliated to the opposition Muslim Brotherhood who tracks online activity.

"They create lots of fake accounts and then they start joining the anti-Mubarak groups and start saying nonsense," said Ahmed Zahran, a protest organiser and cyberactivist.

"Their comments are usually very aggressive which exposes them quickly," he told AFP.

A spokesman for Mubarak's National Democratic Party denied the existence of a centralised campaign.

"There are several Facebook pages created by the youth of the party, who are active on other websites in trying to convey our message," Tarek al-Rifai said.

"It is not a centralised campaign, but a spontaneous effort by the youth. "Sometimes the youth have a different style than the older ones," he told AFP.

But for every pro-Mubarak comment, there would be dozens of counter arguments.

"Every time someone posted something against the protests, we quickly organised ourselves to reply," Ibrahim, an Egyptian computer engineer and cyberactivist, told AFP.

On January 28, Egypt's four main Internet service providers cut off access to their customers in a bid to break the momentum of the demonstrations. It was restored five days later after the ban attracted global condemnation.

Around 23 million Egyptians have either regular or occasional access to the Internet, according to official figures, more than a quarter of the population.

The shutdown in Egypt was the most comprehensive official electronic blackout of its kind that cost the country $18 million per day, experts said.

Facebook, which has about five million active users in the country, expressed concern at the shutdown.

But Google and Twitter went considerably further, jointly creating a tool to allow Egyptians to bypass the Internet closure and post messages to Twitter by making telephone calls.