Either manually or automatically (via a software program) adding low value or no value comments to other sites.

Automated blog spam:

Nice post!
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Manual blog spam:

I just wrote about this on my site. I don’t know you, but I thought I would add no value to your site other than linking through to mine. Check it out!!!!!
cluebag manual spammer (usually with keywords as my name)

As time passes both manual and automated blog comment spam systems are evolving to look more like legitimate comments. I have seen some automated blog comment spam systems that have multiple fake personas that converse with one another.

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