Fifty-four per cent of people questioned by security firm Sophos admitted illegally connecting to someone else's Wi-Fi network.
Logging onto a wireless network without the owner's knowledge or permission, a practice known as 'piggybacking', is illegal in the UK and there have been successful prosecutions for it in the past.
"Stealing Wi-Fi internet access may feel like a victimless crime, but it deprives ISPs of revenue," said Graham Cluley, senior technology consultant at Sophos.
"Furthermore, if you've hopped onto your next door neighbours' wireless broadband connection to illegally download movies and music from the net, chances are that you are also slowing down their internet access and impacting on their download limit," he continued.
Sophos emphasised the importance of securing your wireless network properly.
"It's essential that your Wi-Fi connection is encrypted and that you have not chosen a password for your router which is easy to guess or crack. The problem is that a lot of Wi-Fi equipment is not properly configured when it comes out of the box, or is a headache to setup," Cluley said.