The US Federal Bureau of Investigation (FBI) has received reports of more than $18m in losses in the past year stemming from the spread of the bitcoin ransomware Cryptowall and its related variants.

A 23rd June advisory from the FBI’s Internet Crime Complaint Center stated that the agency received 992 complaints related to Cryptowall between April 2014 and June 2015.

Cyberattacks involving Cryptowall and other types of ransomware encrypt data on the target’s computer, holding that information hostage unless a ransom – generally in bitcoin – is paid. Targets in the past have ranged from law enforcement offices to public schools.

In many cases, the losses incurred by victims have stemmed largely from post-attack costs, according to the advisory.

The notice read:

“The financial impact to victims goes beyond the ransom fee itself, which is typically between $200 and $10,000. Many victims incur additional costs associated with network mitigation, network countermeasures, loss of productivity, legal fees, IT services and/or the purchase of credit monitoring services for employees or customers.”

The advisory stated that the majority of the attacks involve ransoms paid in bitcoin, adding that the digital currency provides a number of useful advantages.

“Criminals prefer bitcoin because it’s easy to use, fast, publicly available, decentralized and provides a sense of heightened security/anonymity,” the notice read.

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