How to disable ads on Skype

You need to add entries to your hosts file, typically located here:C:\Windows\System32\drivers\etc\hosts

These are hostnames you'll want to block, by adding them to the hosts file:

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

Source of hostnames here: wikiHow, and Skype forum. Just a warning, but Microsoft Security Essentials (MSE) may think your hosts file was hijacked, so if you have issues make sure to allow the changes through MSE.