Hackers are taking over computers to mine for cryptocurrency, with cyber-security firm Kaspersky saying Singapore has had a spike in cryptojacking attempts in the first three months of this year.

The firm said it blocked more than 11,700 cryptojacking attempts on devices here between January and March - an increase of more than three times from the same period last year, when there were about 2,900 attempts.

Cryptojacking is the unauthorised use of someone else's device to mine for cryptocurrency by solving complex mathematical problems.

In a recently published report, Russia-based Kaspersky said the spike in Singapore is the highest percentage increase in South-east Asia.

Hijackers target Singapore because its information technology infrastructure offers a healthy supply of bandwidth for cyber criminals to take advantage of.

"Cyber criminals use various means to install miner programs on many people's computers, and take all of the profit from cryptocurrency mining without incurring any of the equipment or electricity costs," said Mr Yeo Siang Tiong, general manager for South-east Asia at Kaspersky.

The hackers rely on social engineering tactics, such as fake links in e-mails or on websites, to dupe victims into installing malicious code onto their devices and wider networks, which turns them into mining tools.

"Miner" computers and devices perform a job similar to a central bank, recording transactions in a ledger publicly accessible to anyone while checking the validity of these exchanges.

For their work, those behind the mining computers are awarded cryptocurrency, which can make the enterprise profitable if the miners can put in the time and energy.

Cyber criminals increasingly prefer cryptojacking to other forms of attacks as it is often more profitable and presents a lower risk of being caught.

The uptick in cryptojacking cases could be due to more people working from home amid the Covid-19 pandemic, said Mr K.K. Lim, head of cyber security, privacy and data protection at law firm Eversheds Harry Elias.

Some of the computers used at home might not have been issued by companies and their security features may not have been kept up to date.

Also, these computers could be shared with other household members, who could have unwittingly downloaded risky programs or visited risky sites, said Mr Lim.

Mr Yeo said many workers might not have the full support of IT security teams working remotely, leading to a lower standard of cyber hygiene during this period.

Has my device been hijacked?

Experts say there are some signs to look out for if one suspects a device has been hijacked for cryptojacking.

"The tell-tale signs for crypto mining can include the slowing down of computer speed, higher consumption of electricity and higher usage of Internet bandwidth," said Mr Bryan Tan, a lawyer from Pinsent Masons MPillay specialising in technology law and data protection.

Mr Yeo Siang Tiong, general manager for South-east Asia at cyber-security firm Kaspersky, said the strain on a device's battery from mining could cause it to physically be deformed too, due to having its processing cores work overtime to obtain cryptocurrency.

He pointed to a recent study by Kaspersky which found that phones that were used to mine for cryptocurrency through malware for two days straight became physically deformed due to the phone batteries expanding.

"Batteries will run down much faster than before, and devices may run quite hot. If the device uses a data plan, users will see data usage skyrocket," he added.

Mr K.K. Lim, head of cyber security, privacy and data protection at law firm Eversheds Harry Elias, said having in place proper Internet browser security features, which can scan for malicious software, will go a long way towards shielding users from falling victim to cryptojacking. But he added that nothing beats practising good cyber hygiene habits such as avoiding unknown links in e-mail and having updated security features.