How long should Google remember searches?

According to Google's Global Privacy Counsel:

"After considering the Article 29 Working Party's concerns, we are announcing a new policy: to anonymize our search server logs after 18 months, rather than the previously-established period of 18 to 24 months." 

Why so long?

• to improve our search algorithms for the benefit of users
• to defend our systems from malicious access and exploitation attempts
• to maintain the integrity of our systems by fighting click fraud and web spam
• to protect our users from threats like spam and phishing
• to respond to valid legal orders from law enforcement as they investigate and prosecute serious crimes like child exploitation; and
• to comply with data retention legal obligations.

[RJ]