Putting anything on the internet exposes your "finite resources" to attackers. I'm sorry, but robots.txt is just a courtesy offered to you, and if you're doing serious business, you shouldn't rely on it. Use authentication, rate-limiting, captchas, DDoS-protecting CDNs, and enforce the limitations at the source, don't rely on nice people respecting your robots.txt.
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Note that serving bots, especially for media-rich sites, eats heavily into a finite resource.
For those of us whose resources are especially tight, blocking Yandex, Baidu and MSN may be very helpful, your ideals notwithstanding.
Putting anything on the internet exposes your "finite resources" to attackers. I'm sorry, but robots.txt is just a courtesy offered to you, and if you're doing serious business, you shouldn't rely on it. Use authentication, rate-limiting, captchas, DDoS-protecting CDNs, and enforce the limitations at the source, don't rely on nice people respecting your robots.txt.