The Advertising Standards Agency (ASA) is checking out a complaint about claims from Microsoft that it can guarantee 99.9 per cent uptime on its cloud services.

The Business Productivity Online Suite (BPOS) has been prone to outages. And even its successor, Office 365, has gone down twice since its launch in late June, leading some customers to dub it "Office 364".

On its promotional material, Redmond says of Office 365: "You can count on Microsoft, an industry leader in productivity, for reliability. Microsoft provides a financially-backed 99.9 per cent uptime guarantee."

The ASA confirmed to The Reg it was "investigating" a complaint over "marketing communication on Microsoft's website".

The ASA said: "The complainant challenged whether the claim that Microsoft Cloud Power could achieve 99.9 per cent uptime was misleading and could be substantiated, because they believed that Microsoft's Cloud Service had not achieved that figure in the year to date."

Downtime of over 8.76 hours a year means Microsoft is liable to compensate customers according to its SLA. It gave BPOS users a 25 per cent credit note last month after a crash caused by a power outage at one of the Dublin-based data centres it uses.

An ASA adjudication will be published once the investigation is complete. The body said: "It may be a few weeks, but equally it may take longer, depending on the complexity of the issues raised."

A Microsoft spokesman told El Reg: "We take our responsibility to deliver reliable services very seriously, and have built Office 365 from the ground up with an updated platform, new infrastructure investments and the latest technology innovations – and Office 365 is backed by the industry's most rigorous financially-backed SLA". ®