Europol is warning people to change the way they use public Wi-Fi hotspots to keep their data safe wherever they browse.
Troels Oerting, head of Europol's cybercrime centre, said the number of people exposing data to hackers was growing and many of these attacks happened via public Wi-Fi networks.
"We have seen an increase in the misuse of Wi-Fi, in order to steal information, identity or passwords and money from the users who use public or insecure Wi-Fi connections," he said.
"You maybe see that your credit card is being misused... but you cannot really capture where it happened," he continued.
Oerting explained to the BBC that you should not access web services - such as online banking - that ask for sensitive information while in a public place or using an untrusted Wi-Fi connection.
This is because criminals are setting up rogue Wi-Fi hotspots, appearing to be part of a public network you'd find in a caf, pub or restaurant, for example. When someone connects to these corrupt networks, the data is transmitted to the hacker.
Oerting said there are steps businesses and the public can take to keep their data safe. For instance, websites that transmit sensitive data should only be accessed via a secure home or business network and only verified Wi-Fi hotspots should be used.
David Emm, senior security researcher at Kaspersky Lab, told The Telegraph that anyone using a public network should ensure the websites they visit display https' in the url, feature the unbroken padlock symbol and carry a valid security certificate.
They should also secure any other device they use to access the internet, with a reputable internet security product.
Last November, the European Parliament was subject to a man-in-the-middle attack, forcing it to close down its Wi-Fi service.
Hackers positioned themselves between the Wi-Fi user and hotspot to siphon off sensitive information, including login details.
It was reported hackers stole the usernames and passwords of 14 people at the European Parliament.
