Internet security experts reacted with scepticism today after Jacqui Smith, the Home Secretary, promised to broaden the online battle against terrorism (write Philippe Naughton and Jonathan Richards).

Ms Smith told a London conference on terror that techniques developed for use against paedophile grooming could be extended to tackle those who use the web to groom young British Muslims to become terrorists.

But security and police experts cautioned that criminals or terrorist recruiters had a vast range of methods at their disposal to conceal their activities and were increasingly sophisticated when it came to evading the authorities.

Ms Smith laid out various measures to counter the "radicalisation into extremism" of young British Muslims to support police efforts against active terror cells.

"Counter-terrorist policing is not just about sharp end - the disruption of those who see to attack us - crucial though that is," she said. "It must also be about stopping people becoming or supporting terrorists, We cannot, after all, simply arrest our way out of the problem."

Speaking at the 'first international conference on radicalisation and political violence', the Home Secretary described the internet as a "key tool for the propagandists for violent extremism".

"Let me be clear: the internet is not a no-go area for government," she said.

"We are already working closely with the communications industry to take action against paedophiles, and together we have improved the way that instances of possible abuse can be reported by internet users.

"If we are ready and willing to take action to stop the grooming of vulnerable young on social networking sites, then I believe we should also take action against those who groom vulnerable people for the purposes of violent extremism.

"In the next few weeks, I will be talking to industry and, critically, those in the community about how best to do this - and how best to identify material that is drawing vulnerable young people into violent extremism. Where there is illegal material on the net, I want it removed."

The online aspect of the counter-terrorist effort was only part of the wider strategy discussed by the Home Secretary, although it garnered headlines even before her speech.

Internet security experts said that it was unlikely that efforts to remove extremist content from the internet would have much impact.

Using advanced technologies such as 'fast-flux DNS', where the location of websites could be shifted around the world on an almost second-by-second basis, extremists could constantly stay one step ahead.

"This type of initiative simply isn't going to have much of an impact on people who want to post and read extreme content," Paul Vlissidis, a security consultant at NCC, said. "Their activities are virtually impossible to police and impossible to trace."

An expert in computer crime at the Met said: "These people are expert at covering their tracks. They hide data within data to conceal their location. They're constantly spoofing their address to hide where they're coming from. It's an ongoing battle."

Meanwhile, internet service providers said that it was not their job to police the internet for offensive comment.

They said they worked with charities such as the Internet Watch Foundation which monitored the web for such content and blocked access to sites hosting illegal content where possible, but that censorship was a job for the authorities.

"If we spent time searching the web's millions of pages for extremist content then we'd do nothing else," Jody Haskayne, a spokesperson for Tiscali, said. "It's not an ISP's job to censor the internet."

A spokesman for the Internet Service Providers Association (ISPA) said that most of the sites concerned were hosted on servers outside of the UK, and were outside the scope of takedown notices that could be issued by British ISPs.

Earlier, Ms Smith told BBC radio that recent cases had suggested growing evidence that people may be using the internet to spread their messages and plan terrorist attacks.

Last October, Mohammed Atif Siddique, a Scottish student, was jailed for eight years for possessing and distributing terrorist material via the web.

Last July, three other men were jailed after pleading guilty to inciting terrorism via the internet in messages that advocated killing non-Muslims.

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