Yahoo said that it will make its user logs anonymous within 90 days as it ups the ante on data retention policies.  In a statement, Yahoo said it would also make user data on page views, page clicks, ad views, and ad clicks anonymous as well as its user logs. The only exceptions would be for "fraud, security, and legal obligations." As for the exceptions Yahoo said:

To protect users and our business partners, there will be some specific and limited exceptions to the anonymization policy. In order to fight fraud and preserve system security, Yahoo will retain system specific data in identifiable form for no more than 6 months--but only for this purpose. Yahoo may have to retain data for longer periods to meet other legal obligations.

Source:→ CNET