VIENNA - Vienna police said on Saturday a "friendly" intelligence service had warned European capitals of the possibility of a shooting or bomb attack before New Year, prompting police across the continent to increase security measures."Several possible names of potential attackers were mentioned, which were checked, and the investigation based on (these checks) has so far yielded no concrete results," Vienna police said in a statement, some six weeks after 130 people were killed in Islamist bombing and shooting attacks in Paris."In the days before Christmas a warning was sent out by a friendly (intelligence) service to numerous European capitals, saying that it could come to an attack involving explosives or a shooting between Christmas and the New Year in crowded spaces."The police asked Austrians for their understanding of the need for more security controls.Extra steps include surveillance in crowded spaces, "especially at events and traffic hubs" as well as intensive identity checks and higher alertness for objects which could carry explosives such as bags or "bicycle frames", it said.Vienna police were not immediately available for further comment.A spokesman for the German Interior Ministry said it did not comment on particular situations for operational reasons."Germany is still in the crosshairs of Jihadist terrorism," he said, adding the country had reviewed and adapted its security measures, where necessary, following the Paris attacks.