More and more people are looking to invest in cryptocurrencies as a result of bitcoin’s recent price surge, but by doing so they could become prime targets for cyber criminals.

Multiple cryptocurrency exchanges have been hacked in the past, resulting in the theft of thousands of bitcoin – which would be worth millions of dollars today.

What’s more, since bitcoin transactions are irreversible, if any of your holdings were to leave your wallet, you won’t simply be able to get a refund.

Fortunately, there are steps users can take to protect their bitcoin.

Security experts recommend storing them offline.

If you purchase bitcoin through an online exchange and choose to store them there too, your security lies in the hands of whichever service you use. If the exchange is hacked – something that isn’t uncommon – the currency you own could be stolen.

That’s because the exchange will hold users’ private keys, long strings of characters that grant access to people’s cryptocurrency holdings. If a hacker managed to get their hands on a private key, they’d be able to steal the bitcoin associated with it too.

“The ever increasing value of cryptocurrencies, especially bitcoin, makes them a very attractive target to cybercriminals, who use various methods to get their hands on them,” malware expert Alexey Malanov, of Kaspersky Lab, told The Independent.

“There have been several huge hacks of cryptocurrency exchanges in the past and the trend will only continue.”

He adds that bitcoin owners “are advised not to store their money on services”.

Users should instead store it offline, on a so-called “cold” wallet, and take care of their private keys themselves.

Something as simple as a USB or an external hard drive can be used as a “cold” wallet.

“The safest way for users to store their bitcoin is to use offline wallets which are not connected to a computer,” Symantec threat researcher Candid Wüest told The Independent.

Gadget and tech news: In pictures Show all 25 1 /25 Gadget and tech news: In pictures Gadget and tech news: In pictures Gun-toting humanoid robot sent into space Russia has launched a humanoid robot into space on a rocket bound for the International Space Station (ISS). The robot Fedor will spend 10 days aboard the ISS practising skills such as using tools to fix issues onboard. Russia's deputy prime minister Dmitry Rogozin has previously shared videos of Fedor handling and shooting guns at a firing range with deadly accuracy. Dmitry Rogozin/Twitter Gadget and tech news: In pictures Google turns 21 Google celebrates its 21st birthday on September 27. The The search engine was founded in September 1998 by two PhD students, Larry Page and Sergey Brin, in their dormitories at California’s Stanford University. Page and Brin chose the name google as it recalled the mathematic term 'googol', meaning 10 raised to the power of 100 Google Gadget and tech news: In pictures Hexa drone lifts off Chief engineer of LIFT aircraft Balazs Kerulo demonstrates the company's "Hexa" personal drone craft in Lago Vista, Texas on June 3 2019 Reuters Gadget and tech news: In pictures Project Scarlett to succeed Xbox One Microsoft announced Project Scarlett, the successor to the Xbox One, at E3 2019. The company said that the new console will be 4 times as powerful as the Xbox One and is slated for a release date of Christmas 2020 Getty Gadget and tech news: In pictures First new iPod in four years Apple has announced the new iPod Touch, the first new iPod in four years. The device will have the option of adding more storage, up to 256GB Apple Gadget and tech news: In pictures Folding phone may flop Samsung will cancel orders of its Galaxy Fold phone at the end of May if the phone is not then ready for sale. The $2000 folding phone has been found to break easily with review copies being recalled after backlash PA Gadget and tech news: In pictures Charging mat non-starter Apple has cancelled its AirPower wireless charging mat, which was slated as a way to charge numerous apple products at once AFP/Getty Gadget and tech news: In pictures "Super league" India shoots down satellite India has claimed status as part of a "super league" of nations after shooting down a live satellite in a test of new missile technology EPA Gadget and tech news: In pictures 5G incoming 5G wireless internet is expected to launch in 2019, with the potential to reach speeds of 50mb/s Getty Gadget and tech news: In pictures Uber halts driverless testing after death Uber has halted testing of driverless vehicles after a woman was killed by one of their cars in Tempe, Arizona. March 19 2018 Getty Gadget and tech news: In pictures A humanoid robot gestures during a demo at a stall in the Indian Machine Tools Expo, IMTEX/Tooltech 2017 held in Bangalore Getty Gadget and tech news: In pictures A humanoid robot gestures during a demo at a stall in the Indian Machine Tools Expo, IMTEX/Tooltech 2017 held in Bangalore Getty Gadget and tech news: In pictures Engineers test a four-metre-tall humanoid manned robot dubbed Method-2 in a lab of the Hankook Mirae Technology in Gunpo, south of Seoul, South Korea Jung Yeon-Je/AFP/Getty Gadget and tech news: In pictures Engineers test a four-metre-tall humanoid manned robot dubbed Method-2 in a lab of the Hankook Mirae Technology in Gunpo, south of Seoul, South Korea Jung Yeon-Je/AFP/Getty Gadget and tech news: In pictures The giant human-like robot bears a striking resemblance to the military robots starring in the movie 'Avatar' and is claimed as a world first by its creators from a South Korean robotic company Jung Yeon-Je/AFP/Getty Gadget and tech news: In pictures Engineers test a four-metre-tall humanoid manned robot dubbed Method-2 in a lab of the Hankook Mirae Technology in Gunpo, south of Seoul, South Korea Jung Yeon-Je/AFP/Getty Gadget and tech news: In pictures Waseda University's saxophonist robot WAS-5, developed by professor Atsuo Takanishi Rex Gadget and tech news: In pictures Waseda University's saxophonist robot WAS-5, developed by professor Atsuo Takanishi and Kaptain Rock playing one string light saber guitar perform jam session Rex Gadget and tech news: In pictures A test line of a new energy suspension railway resembling the giant panda is seen in Chengdu, Sichuan Province, China Reuters Gadget and tech news: In pictures A test line of a new energy suspension railway, resembling a giant panda, is seen in Chengdu, Sichuan Province, China Reuters Gadget and tech news: In pictures A concept car by Trumpchi from GAC Group is shown at the International Automobile Exhibition in Guangzhou, China Rex Gadget and tech news: In pictures A Mirai fuel cell vehicle by Toyota is displayed at the International Automobile Exhibition in Guangzhou, China Reuters Gadget and tech news: In pictures A visitor tries a Nissan VR experience at the International Automobile Exhibition in Guangzhou, China Reuters Gadget and tech news: In pictures A man looks at an exhibit entitled 'Mimus' a giant industrial robot which has been reprogrammed to interact with humans during a photocall at the new Design Museum in South Kensington, London Getty Gadget and tech news: In pictures A new Israeli Da-Vinci unmanned aerial vehicle manufactured by Elbit Systems is displayed during the 4th International conference on Home Land Security and Cyber in the Israeli coastal city of Tel Aviv Getty

Strangely enough, one of the best defences available is paper.

Experts recommend keeping their private keys off a computer or online service. Writing it out on a piece of paper could actually offer better protection, as long as it is stored in a safe place.

If a user was to lose it, however, they won’t be able to access their bitcoin either.

Cameron and Tyler Winklevoss, who own hundreds of millions of dollars worth of bitcoin, store their fortune on a “cold” wallet. They also keep their private key offline, and say they’ve cut the piece of paper it’s printed on into several pieces, which are stored in banks around the US.

Kapersky Lab’s Mr Malanov believes cryptocurrency services should divide deposits into “hot” and “cold” wallets, to protect investors.

“The ‘hot’ wallet should store a minimal amount for daily withdrawals in automatic way, while the ‘cold’ wallet should store the rest of the money and should be operated manually and accessed only when the ‘hot’ wallet has not enough funds left,” he says.

“We also recommend protecting the ‘cold’ wallet with multiple signatures so that only several owners jointly can move the money. Each user holding only one key out of several will keep the money safe.”

Bitcoin can also be stored on a hardware wallet, the likes of which are sold by the likes of Trezor or Ledger. They’re designed to be straightforward to use, and offer additional layers of protection in the form of PINs and seeds.

“As long as the wallet is not connected to a computer, it is safe from attacks as well,” says Mr Wüest.

“But users should pay attention and only buy these devices from trusted sellers, as there have been cases where the device itself has been compromised before it was sold.”

While this method is secure, it comes at the cost of convenience.

“The downside of this method is that it often takes a while to be able to re-activate the bitcoin so if its value drops, users might not be able to react quickly,” says Mr Wüest.

As suggested by Mr Malanov, a sensible move for investors could be to transfer the main bulk of their holdings to a cold wallet, but keep a small amount that they’d be prepared to lose on an exchange service.

“You should use strong passwords to access these wallets, and if you do plan to use a hardware wallet be sure to actively monitor security research to determine if it is as secure you think it is when you purchased the item,” says Raj Samani, McAfee fellow and chief scientist.