Shadow Home Secretary David Davis said the risk of cyber-attack by criminals, foreign governments and terrorists was "serious, strategic and long-term".
But he accused ministers of treating it as a "second order" risk in their security strategy released last month.
He said the Tories would appoint a dedicated cyber-crime minister and a new police unit to fight e-crime.
In a speech to Microsoft's law enforcement conference, Mr Davis said the average citizen "fears e-crime more than theft, mugging or burglary".
But he said "nine out 10" offences went unreported because "in the words of the Metropolitan Police Authority 'there is an unspoken public perception that e-crime is so pervasive that the police service does not have the capacity to investigate each individual allegation".
Mr Davis - a self-confessed "geek" who studied computer science in the late 1960s - said there needed to be a "shake-up in attitudes, strategy and the whole mindset of government on cyber-crime".
He said the closure of the national high-tech crime unit, whose functions have been taken over by the Serious Organised Crime Agency had left a "yawning gap" in Britain's cyber-crime fighting ability.
He said: "The stark reality is that the looming threat of cyber-crime, to the average citizen, to business and to government dwarfs our state of readiness".
He added that the "government do not regard the threat of cyber-attack as a strategic security challenge - just one of several global trends, a second order driver of insecurity.
"I disagree. The risk of cyber-attack by criminals, foreign governments and terrorists is a serious, strategic long-term threat to Britain.
"The government's failure to recognise it as such makes it part of the problem."
He said a Conservative government would "be honest about the scale of the threat" and appoint a dedicated minister to coordinate strategy.
In a Green Paper published last month, the party set out proposals for a new police cyber-crime unit and dedicated Fraud and Cyber Crime Complaint centre to provide the public with up-to-date information.
Last year, an influential group of peers accused the government of putting its "head in the sand" after it rejected their ideas for dealing with e-crime.
The Lords Science and Technology Committee report found the internet was "the playground of criminals".
And it said that the government's "Wild West" approach of leaving internet security to individuals was "inefficient and unrealistic".
The government did not agree with its suggestion that lawlessness "was rife" on the internet - and did not want to add to the burden on industry by passing more regulations.
IT chiefs at some of the UK's biggest companies have also accused the government of failing to take e-crime seriously.
Members of the Corporate IT Forum have called on the Home Office keeps a promise to establish a police unit to deal with high-tech criminal gangs.
The Home Office has said it takes the issue "seriously" and has allocated funding to make reporting cyber-crime easier.