Good news, everyone: Ransomware declining. Bad news: Miscreants are turning to crypto-mining on infected PCs

For the past few years, ransomware has been a bane of computer users. These software nasties infect PCs, scramble files, and demand payment in cryptocurrency to restore the documents.

Those cryptocurrencies are a right faff to get hold of and transfer to miscreants at short notice. And there's no guarantee crooks will hand over the decryption key. And antivirus and operating systems are getting much, much better at blocking ransomware infections. As such, people either don't pay up, or don't need to.

It's therefore no wonder that criminals are cutting out the middle person – the human victim – and infecting machines with remote-controlled malware that quietly mines alt-coins and slips the digital dosh back to its masters.

A single hijacked box can typically mine about 25 cents of Monero a day. Multiply that over tens of thousands of machines, and it adds up to a nice little earner. According to security researchers, criminals are shifting from coining it with ransomware to raking it in directly with stealthy miners.

A Monero miner that's injected by hackers into Windows-powered computers using the NSA's stolen and leaked EternalBlue exploit has netted its overlords $2.8m to $3.6m, according to infosec biz Proofpoint today.

This massive remote-controlled network of mining bots, dubbed Smominru, is churning out roughly 24 XMR ($8,500) a day, we're told. The botnet has press-ganged something like 526,000 Windows boxes, which are mostly servers and mostly in Russia, India, and Taiwan. Two dozen or so computers crawl the internet for vulnerable devices and hijacks them using EternalBlue, which attacks Windows network file-sharing services.

At the end of last yer, Panda Security also found a similar EternalBlue-wielding Monero mining network, dubbed WannaMine after the WannaCry ransomware that famously used the NSA's exploit.

You're havin' a bubble, mate

Cisco's Talos security team has also seen a marked increase in covert cryptocurrency miner installations. The top five digital-coin-crafting operations found by Talos have been similarly making serious bank – up to $330,000 a year in just one case. The rewards are potentially even greater considering the bubble online currency prices are still in.

"The number of ways adversaries are delivering miners to end users is staggering. It is reminiscent of the explosion of ransomware we saw several years ago," the Talos team said on Wednesday. "This is indicative of a major shift in the types of payloads adversaries are trying to deliver. It helps show that the effectiveness of ransomware as a payload is limited."

The thing about ransomware is that it's easy for security tools to detect and block: just look out for programs that start working their way through filesystems to encrypt the contents of documents. No normal everyday application behaves like that.

Currency crafting software, on the other hand, doesn't do anything obviously weird apart from consuming some processor time. Monero mining is ideal for covert crooks because it doesn't require a lot of processing oomph, meaning it can be done in the background with the victim none the wiser.

The miner has to contact an outside server to transfer out its coins, though, which a network admin can detect. Some mining code – particularly Coinhive's widespread JavaScript – is stopped by antivirus packages and ad-blocking tools, so mineware will have to disguise or use fresh cryptographic software routines to avoid detection.

To get a miner onto a computer, a victim is typically tricked into opening that old chestnut of a booby-trapped Word or some other Office document. When opened, the malicious file downloads the mining software from online storage, and gets to work.

Exploit toolkits are also getting mining code to inject into infiltrated systems. The Talos team reported that the RIG exploit kit now has a miner on offer, and one miscreant was pulling in $85 a day using the system, which may not sound like much but adds up to $31,000 a year, tax free.

The only sign that a miner is installed is an increased CPU load on the infected machine, and the occasional transfer of coinage out of the system. Miscreants can configure their malware to send back mined coins daily, but that increases the chance of detection. Leave it too long between deposits, however, and all that sneaky coinage could be lost if the infection is spotted.

Not all miners are as smart as others. The Talos team found one inept CPU-cycle thief who was installing open-source mining code called NiceHash Miner, which is on GitHub. The crook forgot to change the default settings in the app, meaning that any coinage mined went to the software's developer, not the idiot sticking it on other people's systems.

Talos recommends enterprises scan their systems for undercover miners and strip them out as soon as possible. ®