Microsoft has laid off its global advertising salesforce, sources have told Business Insider.

The layoffs — within the Microsoft Advertising division — are expected to affect staff members across the US, UK, and other global offices, charged with selling advertising space across Microsoft's MSN, Bing, Xbox, Outlook, Skype, and Windows 8 properties.

Sources have told Business Insider it was announced Wednesday that Microsoft was making its Microsoft Advertising global sales team redundant as part of the largest sweep of job cuts in Microsoft's history announced this summer, which is understood to affect up to 18,000 roles across the entire business.

One client-side marketer told Business Insider their company had a campaign lined up with Microsoft, only to be informed its account managers at Microsoft Advertising had been told to down tools earlier this week.

A Microsoft spokeswoman told Business Insider: "We've taken another step that will complete almost all the 18,000 reductions announced in July. The reductions happening today are spread across many different business units, and many different countries.”

We asked for more clarification on which divisions are affected, but Microsoft said it had no further information to share.

Tech news website CRN.com reported earlier this week that Microsoft Advertising had shut down its global agencies and accounts team, which handle all of Microsoft's relationships with top advertising agencies and brand-side marketers, as well as Yarn, an in-house creative team responsible for keeping marketers up to date with the latest updates to its advertising formats.

But Business Insider understands the cuts go far deeper than that and will see the departure of the majority of the global salesforce.

The Microsoft Advertising executive team is headed up by Frank Holland, corporate vice president of advertising and online. Business Insider understands all or at least the majority of the Microsoft Advertising executive team listed on the division's website were not affected by the announcement on Wednesday.

Keeping the executive team on board means there is effectively still a sales team in place and it could mean that Microsoft Advertising is streamlining to favor negotiating larger partnerships with key brands, rather than concentrating selling large volumes of display inventory across its network.

However, the closure of Microsoft Advertising has been speculated on for some time. The company had just a tiny 2.45% share of the global display advertising market last year, according to eMarketer. The market is dominated by Google (with a 31.92% share and Facebook, with a 5.82% share.)

The most pertinent sign Microsoft might have looking for an exit from the advertising sector recently was the sale of its Atlas online advertising server to Facebook last year. Shortly afterwards, Microsoft's general manager for display advertising in its online services division, insisted in a blog post the rumors had spiraled out of control. But almost a year later, it looks as though they could be true.