I never believed that an instant messenger is secure. I don’t use my Yahoo Messenger now because I’m afraid of the virus I might receive. I trust Skype but the recent bug which left Skype users sending messengers to the wrong recipients is a bit scary.
You see, after the recent update last month, some users reported that instant messages have been sent to the wrong people in their list. Luckily, I’m not a victim (or did my Skype unintentionally send a message?).
Skype knows about this and is already trying to fix the bug.