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Not sure if anyone was having this problem, but here's what worked for me: Go to "chrome://settings/browser", and then click "Manage search engines". Select ANY other Search as your Default (Google, I'd assume..), and then you should be able to mouseover Blekko, and click the "X" to delete it. It won't let you delete it, if it's still selected as your Default search engine.
Mine was definitely linked to CNET; didn't see it at all, until I downloaded a program from there. That's a shame. But so far, it hasn't come back since I did the above.