The incidents, the details of which are not available for security reasons, have been carried out in public in the center of the city, the prestigious St. Steven's Square (Stephansplatz).
The full notice is as follows:
Be aware of trickery crime. An incident was reported yesterday in which conference delegates were targeted by thieves at the Stephansplatz area in the First District. The delegates were initially stopped by a man asking for directions.
Shortly afterwards two unknown persons in plain clothes, claiming to be police officers, confronted them and asked to see their passports and wallets/purses. The delegates complied with the request, and shortly after the items were returned, they noticed that money had been stolen.
Do not hand over any valuables (wallets, passports, etc.) to unknown persons in plain clothes claiming to be police officers. They try to distract you, e.g. by telling you that you have just spoken to a dangerous criminal and may present fake police badges.
Should you find yourself in such a situation, always request to see both a police badge and an official police ID (a sample copy of both is attached). Always report such incidents to the local police on 133 or 112.