Tens of thousands of organisations have been caught out by a computer virus called WannaCry.
The malicious software locks data away and demands a payment of up to $300 (£230) a time before it will restore scrambled files. In the UK, many hospitals fell victim and some health organisations diverted ambulances and cancelled non-essential services as they sought to contain and clean up the infection. Infections in more than 99 nations are being reported by security firms. It appears that the hardest hit are Russia and Spain.