Yahoo! In the process of running a Search Index Update
Some time ago, there had been reports by multiple users of massive ranking updates in Yahoo’s SERPs (Search Engine Result Pages) due to a possible update. Now Yahoo! has announced that it is in the process of running a Search Index Update for its crawling, indexing and ranking algorithms. This could mean more erratic changes in the page rankings and page shuffling in the index.
Recently, many users had complained to Yahoo! regarding some issues with ‘Deletion of URLs’ in the Site Explorer. According to Yahoo!, this problem has now been resolved.

April 24th, 2008 at 1:01 am
[...] Yahoo! has announced that it will be rolling out a Search Index Update for its crawling, indexing and ranking algorithms. This could explain the weird page ranking changes that happened some days ago and had been reported by a lot of users. More… [...]