The prime minister was last week rebuked by a watchdog for claiming crime had fallen by 14%, which is only correct if fraud is excluded.
He was accused by Sir Keir Starmer of "turning a blind eye to scammers" at Prime Minister's Questions.
Mr Johnson said the government "hates online fraud" and was tackling it.
But he rejected a call by Lib Dem leader Sir Ed Davey to "correct the record on crime figures and apologise".
Sir Ed said Janet, a 74-year-old woman, had told the BBC she had £25,000 stolen by fraudsters.
He said: "For Janet, and for the four million people who fell victim to fraudsters and scammers last year, fraud is a crime."
He asked the prime minister if he and his ministers understand the "hurt" they cause fraud victims when they "write them out of the crime figures and dismiss fraud as something people don't experience in their day-to-day lives".
Janet was one of 69 known victims of a scam which has seen criminals steal £3.9m since 2018 - but only one of their cases has been investigated, an investigation by BBC Radio 4's Money Box discovered.
The prime minister said Sir Ed "knows very very well that this government hates fraud, it hates online fraud."
He added: "We are tackling the scammers by helping people to come forward when they get an email, when they get duped, of course we are helping them in any way that we can.
"But we are also cutting the crime that affects people up and down our country, the neighbourhood crime, dealing with the county lines drugs gangs."
In last Monday's Commons debate on Sue Gray's report on lockdown parties in Downing Street, Mr Johnson said crime had come down by 14%.
But watchdog UK Statistics Authority (UKSA) said the PM "did not make clear" the figure excluded fraud.
It also criticised the Home Office for presenting the latest crime figures for England and Wales in "a misleading way" in a press release.
In its full report, the Office for National Statistics found a 14% increase in total crime in the year to September 2021, driven by a 47% increase in fraud and computer misuse, which surged during lockdown.
But crime excluding fraud and computer misuse decreased by 14%, largely driven by an 18% decrease in theft offences, the ONS said.
On Sunday, Business Secretary Kwasi Kwarteng defended the prime minister's use of statistics.
He told the BBC the prime minister had been talking about "crime that people experience in their day-to-day lives", which "in terms of burglary, in terms of physical injury, has gone down".
His words were seized on by financial campaigner Martin Lewis, who accused Mr Kwarteng of "denigrating the experience of fraud victims" and "the lives that have been lost or destroyed because of scams".
At Prime Minister's Questions, Sir Keir Starmer said: "We've had lockdown for the last two years. Two crimes that people could commit were online fraud and throwing parties.
"As far as I can see, the numbers for both of those have gone through the roof."
He accused Mr Kwarteng and the PM of insulting the victims of online fraud by suggesting it was "not a real crime".
The prime minister replied: "We're investing more into in tackling fraud but we're also tackling the neighbourhood crime that is of such massive psychological damage to people in this country."