Unemployed people will be forced to join up to a government site at the centre of security concerns - as well as posting their CVs online - or face losing their jobseeker’s allowance from the new year, it has been announced.

The Universal Jobmatch site was criticised after hackers demonstrated its vulnerability to attack and Secretary of State for Work and Pensions Iain Duncan Smith admitted that thousands of fake job adverts had been blocked, but that some had got through and had to be removed.

But, speaking this morning, Mr Duncan Smith said that joining it would become compulsory, regardless of whether or not they search for jobs via other means. He said: “We have been clear that this is not mandatory yet and there will be no sanctions for not joining…but mandation will begin in the new year.”

The removal of benefit payments will be at the discretion of job centre staff. But some jobseekers have complained that they do not want to upload sensitive information – such as that included in their CV – to a site over which there have been security fears.

Channel 4 News reported last month that a group of hackers managed to get personal details from dozens of job applicants signed up to the site, including passwords, national insurance numbers and even scans of their passports.

And a host of fake adverts have also appeared on the site. “I signed up and found two interesting items for ‘Mystery Shopper’. One seemed fine but the other was clearly a scam aimed at identity theft,” said one 46-year-old Welshman, who did not want to be named for fear of sanction.

A group of unemployed people came forward to tell the Independent that Job Centre staff are already forcing jobseekers to sign up to the site, which allows them to monitor job searches and remove benefits if they are not deemed sufficient. Some said they believed it was going to be used to take away those payments, regardless of whether or not they were genuinely looking for jobs.

Melissa, from London, said: “I overheard two advisers talking about a man they had just seen and the staff member whose claimant he was said she was going to use his not signing up to the site as an excuse to suspend his money. She said this with relish and it made me sick.”

The site has been set up by recruitment firm Monster, which is being paid £16.7m for its services. Iain Duncan-Smith said he thought it would “revolutionise” the job search process and added that job advisors are able to impose sanctions such as “mandatory work activity” if they feel the unemployed are not searching hard enough.

A DWP source revealed that staff are looking into how to make the site more secure, adding that it was an “ongoing process”. Mr Duncan Smith admitted that some job centre staff had got the wrong idea about whether or not the site was compulsory but a source said that the Department would be making their plans clear.

A DWP spokesman said: “Universal Jobmatch marks a revolution in how we match jobseekers with employers - and vice versa. Nearly 700,000 jobseekers have already registered to use the site and we expect that number to keep on rising.

“Use of the site is not currently mandatory, and the feedback we've had so far from jobseekers is incredibly positive.