Crypto-thieves have earned a total of $175 million in Monero via malicious cryptocurrency mining techniques, according to a recent study. These illicit profits represent 5 percent of all Monero in circulation today.

This surge is largely due to cybercriminals’ preference for the digital currency and the rapid proliferation of crypto-mining malware, the study found. However, since they didn’t include JavaScript or web-based mining activities in their research, the report’s authors noted that the true figure is likely much higher.

Monero: Cybercriminals’ Favorite Digital Currency

For the report, Palo Alto Networks used a threat analysis service to determine which digital currencies malicious actors prefer to mine for and how lucrative this activity is for crypto-miners. Of the 629,126 malware samples included in the research, 531,663 (approximately 85 percent) delivered software designed to mine for Monero. This figure dwarfed that of bitcoin, which came in second with 53,615 samples.

Monero’s dominance extended to the number of wallets observed in the dataset. In total, the researchers identified 2,341 Monero wallets, which was more than twice the amount of bitcoin wallets at 981. By comparison, Electroneum, Ethereum and Litecoin were barely represented at just 131, 44 and 28 wallets, respectively.

In addition, the researchers identified 3,773 emails used to connect to mining pools and 2,995 mining pool URLs.

Addressing the Cryptocurrency Mining Threat

Josh Grunzweig, senior malware researcher at Palo Alto Networks, noted that it’s difficult to defeat cryptocurrency mining software delivered by malware.

“Many malware authors will limit the CPU utilization, or ensure that mining operations only take place during specific times of the day or when the user is inactive,” Grunzweig explained. “Additionally, the malware itself is delivered via a large number of methods, requiring defenders to have an in-depth approach to security.”

To help organizations protect themselves, Palo Alto provided all Monero wallets and hashes for all the malicious samples it identified in its research.