While I cannot explain how this happened, please do see this: https://support.skype.com/en/faq/FA10384/Why-has-m
I also refer fellow Skype users to this detailed information compiled by VooDooDoll:
I trust you have also already alerted your credit card issuer of the unauthorized charges.
Good for you that you pro-actively changed your login (password).
elainem77: Thank you for the descriptions and guidance.
Sofar all OK and I have discovered my account was hacked since January 2012, however it was used briefly and then the hacker used the exisiting credit card details to top it up for more calls. This card is now cancelled.
I have scanned my computer and will monitor my account on daily basis.
Thank you again for your feedback
You are most certainly welcome! 'Tis my pleasure.