A lot of people are able to capture ACARS messsages from published VHF frequencies, download and decipher them. One loon or nutter - take your pick - in Sydney goes so far as to regularly post what he considers 'unusual' ACARS messages on a web-site relating to aviation based on Sydney Airport. The plain language remarks are
highlighted, and have even included private e-mails sent by Air New Zealand crews. Talk about an invasion of privacy!
So, be warned and think twice about any flippant comments or anything that may be sensitive on ACARS as you will never know where the messages end up.