London, May 2 : Ukraine's fighter pilots are vastly outnumbered by the Russians, and have become legendary -- thanks in part to the story of an alleged flying ace called the "Ghost of Kiev", BBC reported. This hero is said to have downed as many as 40 enemy planes -- an incredible feat in an arena where Russia controls the skies. But now the Ukraine Air Force Command has warned on Facebook that the "Ghost of Kiev is a superhero-legend whose character was created by Ukrainians!", BBC reported. "We ask the Ukrainian community not to neglect the basic rules of information hygiene," the message said, urging people to "check the sources of information, before spreading them". Earlier, reports had named the ace pilot as Major Stepan Tarabalka, 29. The authorities confirmed that he was killed in combat on March 13 and honoured with a Hero of Ukraine medal posthumously. Now, the air force stresses that "Tarabalka was not 'Ghost of Kiev', and he did not hit 40 planes". It describes the "Ghost of Kiev" as "a collective image of pilots of the Air Force's 40th tactical aviation brigade, who defend the sky over the capital", rather than a single man's combat record. For weeks, Ukrainians did not have a name to go with the "Ghost of Kiev", but that did not stop the story from going viral on social media, BBC reported. Military experts told the BBC they doubted that one pilot could have downed as many as 40 Russian planes. Ukrainian military historian Mikhail Zhirohov described the Ghost of Kiev story as "propaganda for raising morale". Speaking to the BBC from Chernihiv, he said that early on in the war, the Russians dominated the Ukrainian airspace, so a Ukrainian pilot "could only shoot down two or three". /IANS