Two people have been cautioned for using people's wi-fi broadband Internet connections without permission.
Neighbours in Redditch, Worcestershire, contacted police on Saturday after seeing a man inside a car using a laptop while parked outside a house.
He was arrested and cautioned. A woman was arrested in similar circumstances in the town earlier this month.
BBC Midlands Today correspondent Dr David Gregory said the cases are among the first of their kind.
He added that if people were using someone else's network to enter illegal porn sites, for example, it would be very difficult to trace them.
The man arrested at the weekend was cautioned for dishonestly obtaining electronic communications services with intent to avoid payment.
He attracted attention from neighbours in the early morning, as he had put up cardboard around his car windows but the light from his computer could be seen through the back window.
West Mercia Police said people with wi-fi should follow security advice given by their Internet provider.
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