Spambots -- Disable links in comments
Spambots are hitting nearly every article posting spam links to "news" articles, then up-voting their comments with hundreds of accounts and replying to force the comments to "Top Comments." I've seen these comments receive 100 thumbs up within seconds of being posted. The links posted could easily be malicious.
If Yahoo! removed the ability to post links in comments, these spambots would likely go elsewhere.