people who are using Skype are clueless about how to configure it for maximum security, especially if they have set up a public chat. The default security settings for Skype are not adequate by any means.
Let me give you some tips. First off, click here for the list of commands you can issue in a Skype window.
If you have a public chat, you absolutely must issue this command:
/set optins +TOPIC_AND_PIC_LOCKED_FOR_USERS
If you don’t do that, then anyone can change the chat topic and/or title.
Also, change your privacy settings to allow only your contacts to call you and send you private messages.
If you have those things in place, you’re somewhat secure.