To those who accidentally/intentionally downloaded shockwave then suddenly realized their Yahoo Messenger is not working, see this as the solution to the problem:
http://www.newbie.org/help/lofiversion/index.php?t508.html
your Yahoo Messenger is crashing i think because of a problem with your flash.ocx file. what i did was i searched my computer for my flash.ocx file, when i found it, it was roughly 768kb.. next to it was a file called swflash.ocx which was 400kb, realising that the flash.ocx file wasn’t functioning i played around a little and renamed flash.ocx to flash.ocx.bak, then copied the swflash.ocx file and renamed it flash.ocx.
this way i’ve got 2 of the same file doing different jobs, it fixed my Yahoo Messenger crash-on-start problem.
the older versions didn’t use shockwave, this is why i think the olderversions are fine.