Cryptocurrency mining attacks are on the rise. This year alone, hackers have infected over 1.65 million computers with cryptocurrency miners in just eight months. Security experts say cryptocurrecny mining Trojans have risen dramatically over the past few years, from merely 205,000 global infections in 2013 to over a million in 2017.

Security researchers at Kaspersky Lab said in August alone they detected "several large botnets" being used by cybercriminals to profit from concealed crypto mining. The researchers also said that Monero and ZCash are the most popular virtual currencies, as the "anonymity of transactions" is attractive to cybercriminals.

The researchers said that according to even "the most conservative estimates" crypto mining hackers could rake in up to $30,000 a month. The researchers found hackers operating a roughly 4,000-strong botnet, whose wallet had transferred a total of 2,289 XMR (Monero), which is equivalent to $249,702 (£188,353).

The researchers added that they recently uncovered a network containing an estimated 5,000 computers that had been installed with Minergate, a legal console miner, without the users' knowledge. While the primary method of installing crypto miners is via adware installers that are distributed by hackers using social engineering techniques, hackers are now also using more sophisticated tools such as the leaked NSA exploit EternalBlue.

"The development of the cryptocurrency market has led to an explosive growth in cases where miners are installed without users' knowledge or consent. This can be explained by the fact that when a new cryptocurrency is emerging, it is much easier to mine and make money from it. Threat actors are on the lookout for ways to use the resources of somebody else's hardware, and often it is regular users who fall victim," the Kaspersky Lab researchers said in a blog.