A fresh strain of Android malware has emerged that locks people out of their phones, then delivers a fake message from the FBI telling them they have broken the law by visiting pornographic websites.

The ScarePakage malware then tries to persuade them to pay a $300 fine to its creators via payment service MoneyPak, according to researchers from security company Lookout Mobile Security.

Describing the malware as "highly concerning" in a blog post, Lookout said that it is launched when users use their Android device to visit a website hosting the malicious code.

They will then be prompted to install an app masquerading as Adobe Flash or anti-virus software. Once downloaded, the app triggers the FBI warning, which users can not escape by navigating away.

If they turn their phone off and on again, the warning will reappear immediately, while as soon as they try to interact with another app for more than 10 milliseconds, they are cut off and returned to the ransomware notice.

ScarePakage looks similar to another malware type called ColdBrother, which was also able to take photos of the victim. For now, ScarePakage appears to be targeting the US.

“ScarePakage is likely created by Russian or other Eastern European authors given language cues used in the application that we observed,” explained Lookout. “Unfortunately, this ransomware is hard to remove if you give this malware device administrator privileges.”

Advice to avoid ScarePakage includes refusing to award downloaded apps "device administrator" status unless you are absolutely sure what they do, as well as only downloading apps from developers you know and trust.

ScarePakage is just one of several new strains of ransomware – named for their demands for money in return for letting them access their devices again – to have emerged in recent months.

Simplocker, which locked up people’s data on their SD card, was one of the most concerning, selling for $5000 on cybercriminal forums.

• How can I keep my Android smartphone or tablet secure?