Steps to block Skype ads (requires Windows Admin)
NOTE: Will render "Skype Home" unavailable. Skype home is not required for full Skype functionality.

1: Run cmd.exe as Administrator
2: Type: notepad %windir%\System32\drivers\etc\hosts
3: Add this to the end of the file

#Block Skype ads
127.0.0.1	ds.serving-sys.com
127.0.0.1	speed-s.pointroll.com
127.0.0.1	rad.msn.com
127.0.0.1	g.msn.com
127.0.0.1	live.rads.msn.com
127.0.0.1	ads1.msn.com
127.0.0.1	static.2mdn.net
127.0.0.1	ads2.msads.net
127.0.0.1	a.ads2.msads.net
127.0.0.1	b.ads2.msads.net
127.0.0.1	ad.doubleclick.net
127.0.0.1	ac3.msn.com
127.0.0.1	ec.atdmt.com
127.0.0.1	msntest.serving-sys.com
127.0.0.1	sO.2mdn.net
127.0.0.1	aka-cdn-ns.adtech.de
127.0.0.1	secure.flashtalking.com
127.0.0.1	cdn.atdmt.com
127.0.0.1	apps.skype.com