Controversial Government proposals to increase digital surveillance in Britain have been announced in the Queen's Speech.
The Home Office wants powers to monitor internet traffic, known as communications data, to keep track of serious criminals and terrorists.
But civil liberties campaigners have described the measures as a "Snooper's Charter" and a "dangerous" invasion of privacy.
Jim Killock, executive director of the Open Rights Group , told Sky News: "We're really worried about these new plans for internet snooping, they represent a huge increase in the amount of surveillance government has that are really not appropriate.
"People need to be suspected before they're surveilled - that's how the law should work, but what the Government's saying is: 'Were going to treat you all as suspects, and ask you to trust us not to abuse that data.'
"These are very dangerous measures - they cross a line, they take us from targeting people that we suspect, to targeting everybody and really lowering the barriers of what the Government can find out about you without going through a court."
The new bill was revealed in the Queen's Speech on Wednesday, and the Prime Minister later addressed MPs on the issue.
It was "difficult and contentious legislation", but David Cameron said it was a matter of updating existing laws to cover new technology.
If the laws had not been updated when mobile phones came into use "there would be many, many unsolved cases", he said.
Mr Cameron told MPs: "I don't want to be the Prime Minister standing at this despatch box saying I could have done more to prevent terrorist acts but we didn't have the courage to take difficult steps."
Criminal justice professionals say the proposals are about keeping pace with the changes in technology - to catch paedophiles and terrorists - not reading your Facebook status.
In a recent operation in Lincolnshire, for example, codenamed Operation Alpine, police found an industrial-sized computer server hidden inside a cottage, which was used in the distribution of millions of images of child sex abuse.
Using that data, four men were convicted in the UK, and the email trail led them to hundreds more suspects worldwide.
Jim Gamble, former head of the Child Exploitation and Online Protection Centre (CEOP) , said: "What if we didn't have legislation that allowed us to keep up with the criminals, and in six years from now we weren't able to investigate rapists, child abusers or terrorists?
"People would be coming back and saying - what were you thinking of? Why didn't you put in the investment to make sure that you at least kept up with the criminal?"
The proposals would involve recording "communications data" - the digital fingerprint of who messaged who, when and where - not the actual content of the communication.
The Home Office says it is just an extension of existing powers to cover new technology, as more and more communication moves online, jeopardising the ability of police and security services to keep pace with criminals.
A recent estimate said 25% of requests for communications data by police and agencies could no longer be met.
But some have questioned the cost and the complexity of the operation this would involve.
Professor Peter Sommer, a digital forensics specialist who has acted as an expert witness in some of the country's biggest terrorism and paedophile trials, explained: "In the old-fashioned telephone, when you make a call, a physical connection is made between you and the person you are speaking to, via a series of switches.
"What makes the internet efficient is that you don't need all those direct lines, you just need one connection - all the information is put into what's called a packet and each packet will contain information about where it's coming from and where it's going to, and then the content of the packet.
"But separating the content from the communications data involves specialist hardware called 'deep packet inspection' as well as all the individual filters you'd need for all the different types of internet services, which will in turn need constantly updating, because as we all know - the internet is constantly changing - so there's a vast ongoing cost we have to contemplate."
The Home Office says it does have the technology to make this work, that the content of messages will not be accessed, and that these measures would only be used during criminal investigations, when they could be justified as "necessary and proportionate".
In other words, those with nothing to hide have nothing to fear.
But civil liberties groups are less than convinced. They say this is a digital line that, once crossed, will give the Government unprecedented access to monitor the internet.