I just discovered the safest and effective way to block Yahoo Messenger Ads.

- NO need to edit the registry.
- NO need for EXE Patches that has Trojans.
- ALL YOU NEED is Notepad.

Block Ads By Blocking the Ad Server:

1. Open Notepad.

2. Open the following file:
C:\Windows\system32\drivers\etc\hosts

3. Add the following line at the end of the text file:

127.0.0.1 insider.msg.yahoo.com

4. Save

5. Finish

[source]

*tested on ym ver.9