Sir Mark Rowley, the Metropolitan Police Commissioner, has told the public if you get a text from the force in the next 24 hours - you have been the victim of fraud.
Scotland Yard's most senior officer acknowledged that the warnings are fraught with problems, because the scam victims are often targeted by text messages purporting to be official bodies.
Scotland Yard will contact 70,000 over the next day after the UK's biggest ever fraud sting brought down a phone number spoofing site used by criminals to scam thousands of victims out of millions of pounds.
Asked on the BBC's Radio 4 Today programme about the problem he faces by sending people a text and those victims thinking it is another scam, Sir Mark said: "There's something slightly bizarre about this, isn't there?
"Which is why we were encouraging people to actually go onto the Met Police website and they'll find the shortcuts and links there to report this.
"So don't respond to any text with dodgy shortcuts and things in it, come through official websites is the best way of doing this.
"But we want to hear from you because the people we message in the next 24 hours have been victims of fraud or attempted fraud and we can stack all these offences against the people we've been arrested."
Members of British law enforcement were part of a global operation to bring down ispoof.cc, a website described by police as an online fraud shop.
They worked with Dutch law enforcement who managed to tap the website's servers in the Netherlands to secretly listen to phone calls.
At one point as many as 20 people every minute were being targeted by callers using technology bought from the site.
Criminals, who found out about the site from adverts posted on channels on encrypted messaging app Telegram, used it to buy technology that allowed them to mask their phone number.
This meant they could trick victims into thinking they were being contacted by their bank and persuade them to pass on personal details that allowed the fraudsters to steal cash.
One victim lost £3 million and the average loss among the 4,785 people who have reported being targeted to Action Fraud is £10,000.
There are thought to be many more potential victims.
Of 10 million fraudulent calls made, 40% were in the United States, 35% were in the UK and the rest were spread across a number of countries.
Around 70,000 UK phone numbers called by criminals who used the site will be alerted by the Metropolitan Police via text message on Thursday and Friday and asked to contact the force.
So far 120 arrests have been made - 103 in London and 17 outside the capital.
These include alleged site administrator Teejay Fletcher, 35, who was arrested in east London earlier this month and is facing criminal charges.
Police said Fletcher, who is alleged to be a member of an organised crime group, was living a "lavish" lifestyle.
The site is said to have made more than £3 million profit.
Metropolitan Police Commissioner Sir Mark Rowley said the number of potential UK victims was "extraordinary", adding: "What we are doing here is trying to industrialise our response to the organised criminals' industrialisation of the problem."
Ispoof was created in December 2020 and at its peak had 59,000 users, allowing them to pay for the criminal software using Bitcoin, with charges ranging from £150 to £5,000 per month.
UK police began investigating the site in June 2021, opting for ispoof as the largest criminal site that was based in the country.
Detective Superintendent Helen Rance, who leads on cyber crime for the Met, said: "By taking down ispoof we have prevented further offences and stopped fraudsters targeting future victims.
"Our message to criminals who have used this website is we have your details and are working hard to locate you, regardless of where you are."
