Bitcoin hackers stole £3.2 million of the virtual currency by accessing secure servers through an unprotected personal computer in an online attack on leading exchange Bitstamp, according to a leaked report.
The report allegedly drafted by Bitstamp investigators pinpointed a personal laptop linked to the exchange computer network as a weak point in security.
The company has declined to comment on the report, which is marked as a confidential document.
Industry experts who claim to have a copy of the report say hackers downloaded 3.5 gigabytes of data from the exchange server to a network in Germany and then on to an unknown destination.
None of the stolen Bitcoin has been recovered.
The report also claims the worker was notified of login attempts on his laptop at Bitstamp while he was away from the site, but he failed to take any action.
Apparently, the laptop was not password protected and hackers had prolonged access to the Bitstamp network enabling them to remove the virtual currency without detection.
The online attack took place earlier this year.
The Bitstamp attack is one of many hacker intrusions into Bitcoin exchanges over recent months that has seen the loss of several million pounds worth of the virtual currency.
Bitstamp has paid compensation to customers who suffered losses. An estimated 18,000 Bitcoin were stolen by the hackers.
Bitcoin is an online currency that is unregulated by any central bank or government agency.
The aim was to make Bitcoin independent of government manipulation, but the intention that attracted so many people to invest in the currency has also shown as a weakness as exchanges holding the currency in the same way banks secure cash have been revealed to have different levels of security.
Hackers seem to have a plan of testing exchanges to exploit security vulnerabilities and those with the weakest have lost millions.
In some cases, exchanges could not cover their losses when suffering fraud or online attacks and were forced to close.
As a result of security issues, the value of Bitcoin has plunged in recent months.
In November 2014, the value of Bitcoin peaked at £627 to the Pound, but now stands at £162.
Meanwhile, a US federal investigator has admitted stealing Bitcoin worth almost £450,000 while working on the infamous Silk Road task force.
The Silk Road was allegedly a hideaway on the internet where crooks could trade drugs, stolen goods and firearms in return for the virtual currency.