If you're getting spam comments with a video in old entries (I got 2 in a community post from 2004 that I'd forgotten about), do not play it! Just delete and report as spam. Details here. List of known bot accounts here.
Well, they're certainly spam and that's enough reason not to click on them. Whether they're malware seems to me to be an open question--I got a bunch of those a few weeks at least ago, so it's not that new a thing and I'd expect there to have been some discussion of it on security sites by now.
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