How can I be safe from intruders?

Hi Guys,
I am in trouble and need urgent help. I am using Windows 7 registered version from Microsoft Using Genuine Key. With It i am also using Kaspersky Internet Security 2012 this is also registered version and Antivirus both are fully updated. My Computer Firewall is on. But today 1 intruder challenge me that I can steal a password at Skype.
And after some time he changed password of my Skype and tell me my original password also send me screenshot of my computer. I am very strange how this is possible i think i am secure but now i am worried. Please any one tell me how this attack is done and how can i become fully safe from these intruders.
Also tell me.
Can intruders see https sites passwords or not?
Regards.
