Home Secretary John Reid has announced that convicted paedophiles will have to add their email addresses and any chatroom personas to the sexual offenders register.
Reid told the BBC that the names could be used to filter out those with criminal convictions from sites popular with young people.
"We have to keep ahead of the game and I want to bring in stronger, broader powers to protect our children," he said.
"We would then be able to set up mechanisms that would flag up anyone using those addresses or those identities to make approaches and contacts through some of the very popular internet spaces used by kids."
Sex offenders currently have to register their name, address, photograph, fingerprints and national insurance number within three days of conviction or release from prison.
The details have to be confirmed annually, and offenders must inform the police before leaving the country for more than three days.
Officers are allowed to take a photograph or the fingerprints of sex offenders on the register.
Graham Cluley, senior technology consultant at Sophos, said: "It would seem a bit easy to change your email address.
"But it could provide another reason for the police to bring a prosecution against people if they set up a new online identity. If they do there's a good reason for the authorities to pull them in."
Cluley cited cases in the US where similar laws have been used to catch spammers. Spam with sexual content in the US has to include the words 'sexually explicit' in the subject line.
Only last week T J Web Productions was fined $465,000 by the Federal Trade Commission for failing to use the term.
The UK move was announced at the start of International Safety Day, organised by the European Safer Internet Network, in which nearly 40 countries will work to highlight safer internet practices.
The day includes a competition for schoolchildren to detail their advice on safe use of the internet, and the winner will get €3,000 to be shared in ICT equipment for their school.
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