Disable Skype ads: 1.) Add hosts to your hosts file 2.) Flush DNS resolver cache (ipconfig /flushdns)

hosts

# On Windows 7, 8, 10 Hosts file is in c:\windows\system32\drivers\etc\hosts
#
# Block Skype ads

127.0.0.1 secure-sin.adnxs.com # On skype 7.*
127.0.0.1 *.adnxs.com # On skype 7.*
127.0.0.1 logi10.xiti.com # On skype 7.*
127.0.0.1 *.everesttech.net # On skype 7.*
127.0.0.1 pixel.everesttech.net # On skype 7.*
127.0.0.1 d.adroll.com # On skype 7.*
127.0.0.1 *.msads.net
127.0.0.1 *.msecn.net
127.0.0.1 *.rad.msn.com
127.0.0.1 a.ads2.msads.net
127.0.0.1 ac3.msn.com
127.0.0.1 ad.doubleclick.net
127.0.0.1 adnexus.net
127.0.0.1 adnxs.com
127.0.0.1 ads1.msn.com
127.0.0.1 ads2.msads.net
127.0.0.1 aka-cdn-ns.adtech.de
#127.0.0.1 apps.skype.com # keep this if you want to see Skype Home.
127.0.0.1 b.ads2.msads.net
127.0.0.1 bs.serving-sys.com
127.0.0.1 cdn.atdmt.com
127.0.0.1 cds26.ams9.msecn.net
127.0.0.1 db3aqu.atdmt.com
127.0.0.1 ec.atdmt.com
127.0.0.1 flex.msn.com
127.0.0.1 g.msn.com
127.0.0.1 live.rads.msn.com
127.0.0.1 msntest.serving-sys.com
127.0.0.1 rad.msn.com
127.0.0.1 sO.2mdn.net
127.0.0.1 secure.flashtalking.com
127.0.0.1 static.2mdn.net
127.0.0.1 static.2mdn.net

apps.skype.com does indeed serve ads. Leaving it unblocked I still got ads, blocking it solved that.

Why is 127.0.0.1 static.2mdn.net repeated twice at the end?
What's the use of ads2.msads.net while you have *.msads.net? The very same question is about *.everesttech.net and pixel.everesttech.net. So is about *.adnxs.com and secure-sin.adnxs.com. And about *.msads.net and ads2.msads.net. By the way, ads2.msads.net was split into a.ads2.msads.net and b.ads2.msads.net and does not exist anymore.
As for logi10.xiti.com and .atdmt.com, I'm afraid, these are not the only ad hosts. Get and grep hpHosts for more. db3aqu.atdmt.com is missing there, though.
My DNS doesn't know adnexus.net and ac3.msn.com.
Finally, are you positive that it's sO.2mdn.net but not s0.2mdn.net? The former does not seem to exist while the latter is listed in the above-mentioned hpHosts.

So, what's left as Skype-specific is
127.0.0.1 *.everesttech.net *.msecn.net *.xiti.com apps.skype.com cds26.ams9.msecn.net db3aqu.atdmt.com

@BrendanJ: in my Windows 10 machine, the ads blocked without uncommenting it.

@StSav012: I didn't check the 127.0.0.1 static.2mdn.net, it's a remnant from original gist.
using ads2.msads.net will block the related ads but using *.msads.net not blocking any ads from ads2.msads.net. Looks like host file didn't work with * regex but I can't 100% sure about this.

I can't confirm the validity of those urls. Currently, didn't have any machine with Windows.

Removing the adds does not remove the add placeholder. This can be removed by going to: %appdata%/skype/YOUR_USER_NAME/config.xml and set all Advert values to 0:

      <AdvertEastRailsEnabled>0</AdvertEastRailsEnabled>
      <AdvertLargeEastRailCutoff>0</AdvertLargeEastRailCutoff>
      <AdvertNorthRailCutoff>0</AdvertNorthRailCutoff>
      <AdvertPlaceholder>0</AdvertPlaceholder>
      <AdvertSmallEastRailCutoff>0</AdvertSmallEastRailCutoff>

@RickR2H +1
@StSav012 +1

Working with only your instructions. Other hosts not needed