There may have been more to the Moriarty hack on the Kiev metro than meets the eye

Last week commuters in the Ukrainian capital of Kiev were bemused when all the screens on the city's metro system were hacked to show pictures of arch-villain Moriarty from the BBC's Sherlock.

Authorities said they had no idea how the still - from a famous scene at the end of the season three finale, complete with the villian's ominous words 'Did you miss me?' - ended up all over the network, or who had carried out the hack.

While fans were delighted with the chilling appearance of actor Andrew Scott on screen, the Sherlock hack is just one of a series of more sinister cyberattacks in the country since the end of last year.

Reuters reports that malware was discovered on network systems - including air traffic control - at Kiev airport this week.

While no damage appears to have been caused because the bug wasn't activated, at the end of December similar malware attacked three different power stations in rural Ukraine, rendering one offline for six hours and leaving 80,000 without power in freezing conditions.

Experts have described the incident as the first known power outage caused by a cyber attack.

US researchers linked the malware to previous attacks from Russia-friendly hacker group Sandworm.

The airport cyberattack malware was reportedly directed from a command-and-control server hosted within Russian borders, although such servers are commonly available for hire.

There is no suggestion at this stage that Russia's government was involved, although the cyber attacks have come at a time of badly strained relations between Ukraine and Russia over a nearly two-year-long separatist conflict in eastern Ukraine.

Ukrainian authorities have said they are reviewing government computer systems' defences, including at airports and railway stations, in wake of the recent security breaches.

Ukraine's state-run Computer Emergency Response Team (CERT-UA) issued a warning on Monday of the threat of more attacks.