[laumars]

Thank you. Maybe the same is true in the UK (where I reside) as well and I was mistaken about it being legal?

I'm not sure if this is the relevant legislation but I've found the following in section 48 of the Wireless Telegraphy Act 2006:

A person commits an offence if, otherwise than under the authority of a designated person—

(a) he uses wireless telegraphy apparatus with intent to obtain information as to the contents, sender or addressee of a message (whether sent by means of wireless telegraphy or not) of which neither he nor a person on whose behalf he is acting is an intended recipient, or

(b) he discloses information as to the contents, sender or addressee of such a message.

Source: http://www.legislation.gov.uk/ukpga/2006/36/section/48