Number of Sites Hosting Cryptocurrency Miners Surges 725% in 4 Months

A new report from security vendor Cyren this week confirms assumptions about the recent explosive growth in the number of websites that host cryptocurrency mining software.

Cyren monitored a sample of 500,000 websites between September 2017 and January 2018 and found a 725% increase in the number of domains running cryptocurrency scripts on one or more pages over that period.

As fast as that growth has been, it's still accelerating. According to Cyren, the number of sites knowingly or unknowingly hosting software for mining cryptocurrency registered a threefold jump between last September and October. It plateaued in November before nearly doubling in December and then doubling again in January.

In other words, half the total increase has happened in just the last two months, suggesting that the growth is accelerating, the company said. A total of 7,281 — about 1.4% of the 500,000 websites that Cyren monitored — ran cryptocoin mining scripts as of January 2018.

Much of the growth is being fueled by the insane run-up in cryptocurrency prices in recent months. For instance, the value of Monero, the most widely mined cryptocurrency at the moment, increased by 250% during the four-month period when Cyren was monitoring the websites.

Tinna Thuridur Sigurdardottir, malware analyst at Cyren, says the sites hosting cryptocoin mining tools include both high-traffic and low-traffic destinations. "Most of the sites we've seen are not in the top 10,000 sites globally," says Sigurdardottir. "But there are instances of top 10,000 sites."

Sites can host cryptocurrency mining tools knowingly or — as in a growing number of cases — unknowingly.

A growing number of website operators have begun voluntarily installing cryptocurrency mining software on their sites as a way to supplement revenues generated by ads. As Sigurdardottir notes, two well-known websites doing this are Showtime and Salon magazine.

The operators make money by allowing the mining software to use the systems belonging to website visitors to mine for cryptocurrency. Some sites alert users to the mining activity, while many others do it surreptitiously.

In many other cases, cybercriminals have begun installing mining tools in websites without the knowledge of the operators. They are then quietly using the computing resources of people visiting these sites to mine for digital currency. 

Mining tools often consume a lot of CPU resources and can seriously affect system performance. Not all cryptocoin miners are scripts, Cyren said in its report. Some are executables that could be used at any time to download and install something other than a cryptocoin mining script.

Cryptocurrency miners are extremely easy for site owners to install and super easy for attackers as well once they've hacked a website through usual techniques, Sigurdardottir says. The proliferation of simple JavaScript code from sources such as Coinhive and other Monero miners like Crypto-Loot and deepMiner makes embedding script on a website relatively simple, she says.

Often, all website owners — or attackers — need to do embed a miner in a site is insert two lines of JavaScript. "Coinhive even offers generic code for a website owner to copy and paste into the website's HTML code, replacing 'SITE_KEY' with their own Coinhive site key," Sigurdardottir notes. "Once the code is embedded, all that is required is a visitor coming to the site and spending time there."

Sigurdardottir says it is impossible to know whether sites that are hosting cryptocurrency mining tools are doing so unknowingly or unknowingly without speaking to each operator individually. But attackers have broken into everything from thousands of government sites to basic WordPress sites to embed mining software in recent months, she says.

One entity that has been making these miners widely available is Coinhive.com, whose Coinhive Monero miner is easily the most widely deployed in-browser miner in use. Though Coinhive by itself is a legitimate mining tool, many anti-malware products have begun blocking it because the tool is often embedded in sites without the site owner's knowledge.

Other less widely distributed miners include Crypto-Loot and Coinhave, both of which are also Monero miners, says Sigurdardottir. "Monero is the most common currency," she says. "Monero bills itself as a 'secure, private, and untraceable cryptocurrency,' employing a technology that makes it virtually impossible to track transactions to any individual or IP address."

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