Quality signals - Prefer authoritative pages based on:

• Votes from authors (linkage signals)
• Votes from users (usage signals)

Policing of URL submissions

• Anti robot test

Limits on meta-keywords

Robust link analysis

• Ignore statistically implausible linkage (or text)
• Use link analysis to detect spammers (guilt by association)

Spam recognition by artificial intelligence

• Training set based on known spam

Family friendly filters

• Linguistic analysis, general classification techniques, etc.
• For images: flesh tone detectors, source text analysis, etc.

Editorial intervention

• Blacklists
• Top queries audited
• Complaints addressed
• Suspect pattern detection