However, there are those who actively seek them out and it is these people who have begun the warchalking craze, leaving symbols with details of network connections for other users.
She added: 'Many argue that warchalking is not theft since theft involves taking something from someone which prevents them from using it.
Using someone's wireless network does not actually 'take' anything but warchalking can be used for harmful activities such as crashing someone's computer, looking at their files or preventing them from using the Internet.
Jeremy Beale, head of ebusiness for the Confederation of British Industry (CBI) said: 'The CBI condemns warchalking as an implicit incitement to irresponsible and illegal acts.
But Ben Hammersley, a freelance writer who says he made the first chalk mark of the craze outside his house in London five weeks ago, retorted: 'The potential use of warchalking for hacking purposes has been highly overblown.