how to prevent indexing by rss directories?

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I've added RSS feeds to my site and I have visited a RSS directory.
I thought they only riview RSS links, but most of those I've visited
report the whole items.

So my actual problem is how to prevent indexing from all RSS directories.
I can indicate it to people, but how to stop all the crawlers?
Are there any directory with listed all RSS directories bots, to ban
them in the .htaccess?

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