While randomly browsing through a talk page on Wikipedia about Yahoo! Messenger, I came across a topic suggesting for the Wikipedia page on Yahoo! Messenger to at least address Yahoo! Chat’s insane amount of spam bots and child predators lurking in mostly adult chatrooms (Yikes!). One of the poster’s references, aside from his own, was a link to a now-defunct site, mentioning that it was a plea by @ChetSimpson, who apparently was the creator of a program named YTunnel.
Wanting to know more about this newly-discovered finding, I went to Google and looked up this YTunnel thing. First result was an article briefly tying Chet to YTunnel, and the second result gave me insight on what this YTunnel thing was. It seems like YTunnel was a program developed by the guy with the intent of supplying anti-booting (for those who don’t know, it’s basically sending specially crafted YMSG packets during Yahoo! Messenger/Yahoo! Chat conversations that cause a buffer overflow in Yahoo! Messenger and basically crash the client), beefed up anti-spam and privacy features, and visual enhancements to Yahoo! Messenger (a few of those visual enhancements being removal of ad banners in chat and webcam windows, enlarging the IM/Yahoo! chatroom window, and filtering font/text effects in conversations for easing computer performance), and some more, which you can read at this archived link.
From piecing everything together, YTunnel seems to be Yahoo!'s Messenger Plus, but more oriented toward making the user’s experience less of a pain than it should be rather than adding fun features to make the client unique. I congratulate @ChetSimpson for making this 15-year-old program that unfortunately faced it’s demise around early 2012 for no given reason, when Yahoo! Messenger was still actively maintained as version 11.5, the last version to be released.
Heck, I’d give it a try, and I’m not exaggerating, given the circumstance of YTunnel, as there are archives of the installers on the Wayback Machine, despite the fact that the program was paid lol. 
Anyways, know that you now have the @Patchou of the Yahoo! Messenger scene.