According to the CBC, the four suspects managed to make over CAD $200,000 ($150,000) through the attacks, in which they managed to conduct 112 fraudulent transactions in seven cities in Canada, half of which in Calgary.
Each of the four suspects is accused of attacks in specific cities.
The men's identities are still unknown, therefor the Calgary police chose to turn to the public to ask for help in identifying the criminals.
Police say the suspects were committing "double-spend" attacks and would visit a bitcoin kiosk and successfully withdraw money before cancelling their transaction before the bitcoin company would process the withdrawal.
Almost half, 51, of the transactions allegedly occurred in Calgary.More news: Opportunity's last gift from Mars is a handsome panorama
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The police asked the public assistance in identifying the people involved in the crimes.
Calgary is home to a total number of 45 Bitcoin ATMs, but only 21 of them support Bitcoin sales. Although the tools were not specifically created for such criminal activity, the tools essentially enable "stuck" transactions become "unstuck" when one pays an extra fee. The objective of 0-conf is to create instantaneous transactions for instances when the 10-minute Bitcoin transaction throughput time would not be convenient.
Authentic double spend attacks either involve exploiting a code defect in a crypto network's software or a "51% attack"(brute force attack) on a cryptographic ledger's processing of transactions. In addition, you can optionally specify that the first transaction additional OP-RETURN, multisig, and "blacklisted" address outputs.
Investigators believe the fraudulent transactions were committed by a group of individuals who were working together and have "in-depth knowledge or interest in cryptocurrency, bitcoin and/or blockchain technology". These ATMs are owned by several companies including Bitnational, Bitcoin Solutions, and Bitcoiniacs, with some of them having daily sales limit of up to $9000.