Google executive and official employee number 20 Marissa Mayer has been appointed the next CEO of Yahoo in a move that appears to have taken the US tech industry by surprise.

Why commentators are surprised is not hard to fathom; Yahoo's business has become synonymous with the word 'struggle', having fired its last CEO, Scott Thompson, in May after a bizarre scandal over his allegedly embellished CV.

In January, co-founder, figurehead and recent CEO Jerry Yang quit the firm after carrying the can for rebuffing a 2008 $44.6 billion (£29 billion) takeover offer from Microsoft that investors (and almost everyone else) now views as good business as well as comically generous. Yahoo is now worth less than half that sum.

Did we mention Carol Bartz? Appointed in 2009, the former Autodesk head was infamously fired over the phone in September 2011 and made no secret of that fact in a parting email to employees.

Into the breach now steps another female head, although one more noted for her engineering background.

"Marissa is a well-known, visionary leader in user experience and product design and one of Silicon Valley's most exciting strategists in technology development,” announced Yahoo's other co-founder and surviving board member, David Filo.

"I am honored and delighted to lead Yahoo, one of the Internet's premier destinations for more than 700 million users. I look forward to working with the company's dedicated employees to bring innovative products, content, and personalized experiences to users and advertisers all around the world," said Mayer herself.

Mayer was most recently responsible for Local, Maps, and Location Services for Google, the part of the search company that includes Google Maps, Google Earth, and Street View. She is strongly associated with Gmail, its toolbar and the general look and feel of the Google product experience.

The general view is that Mayer had to leave Google to be anything other than a marginal player, even if that meant taking on a fading and increasingly irrelevant star of the long-gone era.

And she has plenty of work to do and not just on the business model. Only last week a data breach saw 400,000 passwords from the company's Yahoo Voice VoIP network were posted online after apparently not being properly encrypted.