When does yahoo and google update their algo?

Hello Guys ..

I am a SEO begginer and have heard that Google and Yahoo use to periodically update their algorithm, when do they use to do such updates?

Thank you...

Search engine updates cannot be predicted beforehand. They really make their algorithms and rules and then they announce their updates.

Yahoo have recently updated their algo and it was a major shake in the yahoo SERPs: hotseonews.net/SearchEngines/Yahoo-search-update/ Google has done a major update in March and now is tuning his algo so basically is continuosly updating.

I think that every year, Google and yahoo changes its search algorithm around 400–600 times. While almost of these changes are minor, but Google occasionally rolls out a "major" algorithmic update (such as Google Panda and Google Penguin and humingbird) that affects search results in significant ways.