A new cyber threat is earning millions for international hacker gangs - 'ransomware' attacks, which blackmail users into paying to get back into their own PCs.
The attacks often use clever 'social engineering' such as warnings which seem to be from local police which say, "You have browsed illicit materials and must pay a fine."
The scam works by using malware to disable victims' computers until they pay a ransom to restore access - a fee of up to £280.
Faced with such scare tactics, security experts Norton by Symantec found around 2.9% of victims end up paying ransoms.
One gang was observed attempting to infect 495,000 computers over the course of just 18 days.
Norton by Symantec, estimate cybercriminals are raking in over £3 million a year from victims as a result of this scam, and that number is likely to grow.
'Ransomware' is one of the fastest-growing areas of cybercrime.
The first of these cyber-attacks appeared in 2009 in Russia and Eastern Europe.
Now the attacks have gone global - becoming highly popular with international online criminal gangs, spreading the threat to Western Europe, the United States and Canada over the past year.