Tam, have just been talking to my son, who is doing IT degree course at Univ.
He reckons the system would be safe enough because whoever set up the software will have been very mindful of security, and will be as safe as sending an ordinary E-mail to someone. As Thimbles has stated, systems can be hacked, although, with all due respect to PB and its' users, we haven't quite reached CIA, FBI or NASA levels where someone would want to spend the time or money to gain access to messages on this site !! It certainly won't give me any problems in sending a PM to someone.