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How does Stack Overflow handle spam?

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  • new user limits (only 1 url allowed in posts, only 1 question per 20 minutes, only 1 answer per 3 minutes)

  • captcha

  • script detection heuristics and "honeypots"

  • user flagging (spam / offensive / moderator attention)

  • auto-removal of some items based on certain flag thresholds being met

  • active moderator participation throughout the day to look at moderator flagged items

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    So why do established accounts still get the captcha occasionally? – Perpetual Motion Goat Jul 6 '09 at 14:18
  • @finnw - it triggers if you post twice in quick succession. – ChrisF♦ Jul 6 '09 at 14:21
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    how will we know if you're a replicant or not? – Jeff Atwood Jul 6 '09 at 14:26
  • "Established accounts" could be picked-up and used by scripts after human-establishment. – Sampson Jul 6 '09 at 14:26
  • What are these "honeypots" that you speak of (in the context of SO, not in general)? – anand.trex Jul 6 '09 at 15:00
  • @trex, Would he dare to tell us about his honeypot? – Johannes Schaub - litb Jul 7 '09 at 12:17
  • @litb , trex279 is an automated bot seeking honey. – Kent Fredric Aug 6 '09 at 8:32
  • @Jeff - I am not a replicant. There, now you know. – Pollyanna Dec 14 '09 at 17:27
  • @Pollyanna: that's what a replicant would say. – perbert Apr 14 '10 at 22:19
  • auto-removal of some items based on certain flag thresholds being met - does this mean Spam-Assassin-style Bayesian filtering? – Charles Stewart May 7 '10 at 13:39
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They use reCAPTCHA to ask for CAPTCHA's if there are frequent actions performed (although this is more a preventative measure than for actually dealing with it).

There are also the moderators in place, who can delete posts that are deemed as spam, and the community, who are the ones who flag posts as spam to get the moderators' attention.

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