If you truly wanting to learn, may I make the following suggestion:

DO NOT CONTINUE DOWN THIS PATH!!!

By attempting this against a live service (which I doubt has provided you with written indemnity), you open yourself up to a number of potential consequences such as (but not limited to):

• being removed from the Skype service (due to violation of their ToS),
• possible loss of your internet connectivity (due to violation of your service provider's ToS),
• if you are at work and doing this, possible job loss (due to violations of computer use or employee policies),
• if you are a student and doing this while attending an educational facility, the possibility of academic penalties such as (but not limited to):
  • loss of access to academic computing resources (if done from a facility device),
  • automatic course failure (if done while in a class),
  • probation, suspension, and/or expulsion (for violation of facility policies and/or codes of conduct),
  and/or
• possible criminal charges (and, depending on geographic locations of you, the servers, and the services involved, the possibility of charges in multiple jurisdictions (for example, in the US the possibility of both state and federal charges)).

Because the code you post has no limitation of misuse other than the content of your user and password lists. As such, under some jurisdictions that in itself may be enough to open you up to the potential of criminal and/or civil penalties. (It may also be enough to have potentially have adverse effects for this site as well, such as having it blocked by a filtering service for hosting potential "cracking" tools.)

IF you wish to learn more about computer (?:in)?security, may I make the following suggestion: there (a|we)re several Linux distributions that were built for exactly the purpose of learning about computer security and penetration testing. I would recommend finding one of those (this query may help you find an appropriate one), install and run it from a local VM, and MAKE ABSOLUTELY SURE YOUR TRAFFIC IS LIMITED TO YOUR OWN NETWORK (or, better yet, your own local machine).

Please understand that while we encourage learning here, those of us who are suggesting you explore other ways of learning computer security are doing so in hopes of helping you by advising you against a course of study that could have effects you have not considered.

Hope that helps.