Has someone got acess to my computer through skype?Do I now have a security problem?

I keep getting these XXXXX wants to access your computer through Skype  . I have chosen allow a couple of times thinking someone I knew was trying to get through.  No one ever rings  or shows up in my contacts. Have I allowed a security breachinto my mac? I got a call from citicard about a security problem and had to have a new card issued. Are these related? Should I be worried about signing in to bank accounts and such? Where do I go in skype to see who has access and Can i "reblock" those addresses that I "allowed" Or were they one time events?