Out of sight, out of mind.

At least, that phrase may be at the heart of a new scheme implemented by The Pirate Bay to generate revenue -- the use of cryptocurrency mining scripts which use power from visitor machines to generate Monero (XMR).

It was back in September that the torrent search website was widely criticized for implementing a cryptocurrency mining pilot scheme.

Despite claiming that the miner only impacted a small number of website visitors, the mining operation -- made possible through a script from Coinhive -- contained a typographical error which sent visitor CPU usage rocketing and caused an absolute uproar.

This led to concerns that the website had been compromised, and when the pilot was uncovered, the Pirate Bay defended its actions as a "small test" to ascertain the viability of mining for cryptocurrency as a replacement revenue generator for advertising.

"We really want to get rid of all the ads," the operators said. "But we also need enough money to keep the site running."

One of the main criticisms levied at the website was the lack of transparency. Visitors were unaware of the program and so were not only hit with standard advertising but also had their CPU power drained.

The lack of an option to opt-in and permit their systems to help mine for cryptocurrency was unacceptable -- but it seems the profits from the pilot have borne fruit.

Now, should you visit The Pirate Bay, you are met with a small notice at the bottom of the page which indicates that moving further into the domain implies consent to joining the cryptocurrency mining pool.

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"By entering TPB you agree to XMR being mined using your CPU. If you don't agree please leave now or install an adBlocker," the notice reads.

The message, albeit small, is a move in the right direction. Cryptocurrency mining has the potential to become a valid alternative to website advertising. The balance between revenue generation and adverts can be difficult to maintain; ads should not be intrusive, they should blend and become seamless, but they also must be placed in spaces prominent enough to placate advertisers.

If adverts disrupt the user experience too much, website visitors may be tempted to download an ad blocker. This may clean up web pages but, in turn, can eradicate profits made from third-party ad networks.

This tightrope, together with estimates that three in ten Internet users will block adverts by the end of this year, has prompted discussions on other ways to generate profit from website visitors.

Paywalls are one way, and subscriptions another, but attempting to apply these barriers wholescale is unlikely to prove successful.

Cryptocurrency mining, however, is unobtrusive, does not disrupt the user experience -- as long as CPU power limitations are in place -- and has the potential to bring in significant revenue.

If cryptocurrency mining is ever to become a significant alternative to ads, however, transparency and user choice must be included.

Without these key ingredients, the use of cryptocurrency mining scripts on website domains is nothing more than cryptojacking.

Cryptojacking is the theft of user power, through in-browser scripts or malicious software, to secretly mine for virtual currencies. Thousands of websites are estimated to be actively compromised with malicious cryptocurrency mining usage, while the February BrowseAloud incident -- in which thousands of government websites in the UK and beyond were compromised to cryptojack visitors -- has highlighted this emerging trend in the cyberattack space.

If website owners chose to secretly implement these scripts and do not seek at least implied consent by informing users of mining operations, they are stealing and this makes them no different to the cyberattackers which plague our existence on a daily basis.

While this practice has the potential to become a legitimate business model of its own -- assuming the cryptocurrency bubble doesn't burst -- the power is still in consumer's hands.

Coinhive can be blocked through ad blocking software. In the same manner as intrusive advertising practices, without balance, users will still turn towards ways to block mining scripts rather than agree in return for using an online service.