Thousands of well-wishers are feared to have been duped into donating to fake fundraising pages for victims of the Manchester bombings.
Dozens of appeals were launched in the wake of Monday's terror attack to support the families of the 22 people who were killed.
But the world's most popular fundraising site GoFundMe yesterday (Fri) announced that it has been forced to suspend two accounts over fears they are fraudulent.
The company confirmed it is investigating a number of pages and has vowed to refund anyone it believes has been tricked.
It is not yet clear which appeals have been affected.
A spokesman for GoFundMe said: "Since the attacks on Monday, we've had people monitoring related campaigns around the clock.
"The overwhelming majority of campaigns which have been started have been started with the very best intentions by kind people trying to do their bit for others.
"In situations like this one GoFundMe engages our emergency procedure - vetting every single campaign to check that they're safe for donors to give to.
"We do this by contacting organisers, making sure they are who they say they are and that they have a clear way of getting the money to the intended recipient.
"If they're not clear on that, we'll help them make that connection, but they won't be able to withdraw any donations.
"If we can't make that clear, the account will be suspended.
"If we spot any suspicious activity on GoFundMe we immediately suspend the campaign and contact the campaign organiser.
"This has happened just a handful of times this week."
Lydia Fairman, of The Mount, York, set up a fundraising page to help the families of the victims pay bills.
She hit out at the con artists who set up the fake pages and said: "It's appalling and a heinous crime. It's exploiting somebody's loss.
"I hope they are investigated and they are found."
She said she has been contacted by GoFundMe and informed that anyone who set up an account for the victims of the attack will not be able to withdraw funds.
They now have the option of keeping the page open or transferring the cash to an appeal set up by the Manchester Evening News, which has so far raised £1.5 million.
Billy Iqbal, a manager at York Cars, set up a fundraising account for one of the victims of the terror attack, taxi driver Marcin Klis.
He said: "At this moment in time it's shocking. We all need to get together and show our support.
"If people are going to take advantage for their own benefit it's bang out of order."
Greater Manchester Police and Action Fraud - the country's fraud and cyber crime reporting centre - have both moved to warn people about fraudulent accounts.
The police force tweeted: "Please be aware of fraudulent fundraising pages on the internet.
"If you wish to donate please use this page - goo.gl/yQV210."