Head of Europol's cybercrime centre is warning companies and individuals not to send sensitive information over public WiFi hotspots.
Troels Oerting told the BBC that man in the middle attacks using public WiFi were becoming the favoured method of attack for hackers.
Oerting said it was difficult to grasp the magnitude of the problem, because you might see that your credit card is being misused but you cannot really tell when and where it happened.
Man in the Middle
He added that there had been an increase in the misuse of WiFi in order to steal information, identity or passwords and money from the users who use public or insecure wi-fi connections.
Article continues below
There was little new about the technology the hackers were using. Normally they relied on well-known approaches that attempt to trick people into connecting to a fake hotspot that, superficially, resembles those seen in cafes, pubs and restaurants and other public spaces.
A few months ago, the European parliament turned off its public WiFi system after it was discovered that a "man-in-the-middle" attack was being perpetrated via the service.
- Now read how major cyber attacks can be predicted