Today's Tech: Bebo announces a dramatic comeback and Windows 8 tops Vista but lags way behind Windows 7, XP and Apple's Mac OS X

Microsoft ended last week's Build developer conference on a high note — the announcement of increased Windows 8 market share. The operating system topped five per cent market share in June, according to stats from Net Applications, finally eclipsing Microsoft's Vista OS. Still, Windows 7 and Windows XP still rule, with 44.37 per cent and 37.17 per cent of the market, respectively. Windows 8 landed at 5.1 per cent last month, up from 4.27 per cent in May. Vista actually also saw some growth - from 4.51 to 4.62 per cent - but still dropped from third to fourth place. Windows 8 isn't exactly a runaway hit, though. The OS sits behind Apple's Mac OS X, which has 7.2 per cent of the overall market.

Unpopular social network Bebo is facing resurrection, following its purchase by one of its co-founders. Michael Birch, who created Bebo with his wife, Xochi, in 2005, took to Twitter to announce, "We just bought Bebo back for $1m. Can we actually re-invent it? Who knows, but it will be fun trying..." The founders originally sold Bebo – which by then boasted 40 million users - to AOL in 2008 for a massive $850 million (£560 million), but things soon turned sour. Due to various issues, including lack of investment and the emergence of Facebook and Twitter, Bebo quickly became irrelevant and was eventually sold on to Criterion Capital and a consortium of individual investors for $10 million (£6.6 million) in 2010. Birch's incubator firm, Monkey Inferno, will be responsible for Bebo's revival, and is reportedly bringing in mobile developers to work on the project.

Zynga has confirmed that Don Mattrick will leave Microsoft to become the gaming firm's new CEO. In a note to employees, current CEO and chief product officer Mark Pincus said that Mattrick will officially join Zynga next week, but will be present at an all-hands meeting at Zynga headquarters this week to answer questions. In reflecting on his time at Zynga, Pincus said, "I realise that I've had the greatest impact working as an entrepreneur with product teams, developing games that could entertain and connect millions. I've always said to Bing and our Board that if I could find someone who could do a better job as our CEO I'd do all I could to recruit and bring that person in. I'm confident that Don is that leader," Pincus said. Pincus will remain chief product officer and chairman of the board. In a letter to employees, Microsoft chief Steve Ballmer said "this is a great opportunity for Don, and I wish him success." For now, those who reported to Mattrick will report to Ballmer, "and will continue to drive the day-to-day business as a team, particularly focused on shipping Xbox One this holiday."

Sainsbury's has joined forces with Vodafone to launch a new mobile phone network that aims to compete with the O2-powered Tesco Mobile and Vodafone-run Asda Mobile. The joint venture, called Mobile by Sainsbury's, will be owned in equal parts by Vodafone and Sainsbury's and will launch later in the summer. An introductory offer of 2,500 Nectar points will be offered to new customers signing up. Sainsbury's already sells SIM cards and smartphones instore, so it makes sense for them to offer an MVNO service. The supermarket has also confirmed that it will sell Apple's iPhone 5 and, in order to make its mark, it will offer the Samsung Galaxy S4 on O2 with 600 minutes, unlimited texts and 750MB data for £32 per month. It remains to be seen whether customers on Mobile by Sainsbury's will be able to use phones locked to Vodafone. It will also be interesting to check out whether other major retailers follow on.