Many Welsh firms do not realise they can be liable for e-crime committed over wi-fi networks they provide, a web safety group has warned.
Hospitality firms in particular are unaware of their responsibilities, says e-Crime Wales.
It said a survey it carried out found almost one in four firms in Wales (23%) have been a victim of this kind of crime in the last year.
Figures out in May showed e-crime was costing around £373m a year.
The warning came ahead of a summit at Newport's Celtic Manor resort.
Advice is being offered on how to avoid becoming a victim of cyber crime, focusing on tourism firms in particular.
The summit is being held at the venue which will host the Ryder Cup golf tournament in October.
Thousands of visitors are expected in the area over the tournament.
But it is also the type of large scale event which attracts opportunistic e-criminals, said the safety group.
Its research shows 75% of Welsh tourism firms did not know the Digital Economy Bill meant the companies were responsible for any criminal activity which used their wi-fi networks.
More than 470 firms are expected at the summit.
e-Crime Wales and Visit Wales are also sending a how-to guide on wi-fi network security to a number of firms.
Andrea Barnard from e-Crime Wales said: "The advice we would give is for firms to secure their wi-fi network with individual key codes, so each client has their own person key.
"If any criminal activity does take place, they would then be aware which client would be responsible.
"But it's general for all businesses, irrespective of which sector they were in."