code: func (ka *KnownAddress) isBad() bool {
  	if ka.lastattempt.After(time.Now().Add(-1 * time.Minute)) {
  		return false
  	}
  
  	// From the future?
  	if ka.na.Timestamp.After(time.Now().Add(10 * time.Minute)) {
  		return true
  	}
  
  	// Over a month old?
  	if ka.na.Timestamp.Before(time.Now().Add(-1 * numMissingDays * time.Hour * 24)) {
  		return true
  	}
  
  	// Never succeeded?
  	if ka.lastsuccess.IsZero() && ka.attempts >= numRetries {
  		return true
  	}
  
  	// Hasn't succeeded in too long?
  	if !ka.lastsuccess.After(time.Now().Add(-1*minBadDays*time.Hour*24)) &&
  		ka.attempts >= maxFailures {
  		return true
  	}
  
  	return false
  }
docs: // isBad returns true if the address in question has not been tried in the last
  // minute and meets one of the following criteria:
  // 1) It claims to be from the future
  // 2) It hasn't been seen in over a month
  // 3) It has failed at least three times and never succeeded
  // 4) It has failed ten times in the last week
  // All addresses that meet these criteria are assumed to be worthless and not
  // worth keeping hold of.