Microsoft is the world's biggest company. That's why when GeekWire obtained an internal Microsoft list of competitors' products that employees aren't allowed to use, people noticed.

What's even more interesting? The surprises in the group.

So here's the list of banned and "discouraged" competitors, ranked in increasing order of pure surprise. (I admit, the first four or so aren't that surprising. But keep reading.)

1. Kaspersky Lab (Prohibited)

We don't have any specific information from Microsoft as to why Kaspersky is on the list. 

However, last summer the U.S. government banned the Russian company's software from being used by contractors working with the Pentagon, the General Services Administration, or NASA.

So we'll rank this one as quite unsurprising.

If the U.S. government refuses to use a Russian company's security software, it's not a big stretch for American companies to fall in line.

2. Slack (Prohibited-ish)

As my colleague Jason Aten writes, it's "probably not all that surprising" to find Microsoft employees mostly prohibited from using Slack, given Microsoft's competing product, Microsoft Teams.

In fact, as Nat Lev and Todd Bishop wrote on GeekWire, Slack listed Microsoft as its primary competitor when it filed to go public. (I'll bet you'd discourage your employees from using your competitors' products, too.)

However, Microsoft says the issue is that the free versions of Slack don't "provide required controls to properly protect Microsoft intellectual property (IP)."  

Microsoft says that Slack Enterprise Grid does comply with Microsoft's security requirements, however, the company does "encourage use of Microsoft Teams rather than a competitive software."

3. Amazon Web Services (Discouraged)

AWS is just "discouraged," not flat-out banned, but other than that small bit of leeway, it's probably not all that surprising to see this on the list, given that AWS is a direct competitor with Microsoft's Azure cloud platform. 

Using it internally requires "a business justification," according to the Microsoft summary. "It is highly recommended to start a migration plan to Azure prior to engaging the Governance team for new request or renewals."

4. Google Docs (Discouraged)

I almost want to rank Google Docs and AWS as a tie, but we'll give the slight edge in surprise to Google Docs, simply because I'd sort of thought the whole Microsoft Office versus Google Docs battle had receded into history. 

But no--Google Docs is "discouraged for use."

5. PagerDuty (Discouraged)

This one is pretty surprising to me, if only because I'd like to quote from a PagerDuty press release one year ago, when the two companies were collaborating:

"Agile incident response is an essential practice," a Microsoft employee who ran the company's Visual Studio Team Services said in the press release. "VSTS integration with PagerDuty helps manage incidents and mobilize the right people to accelerate resolution and complete the DevOps loop."

6. Grammarly (Prohibited)

Highly surprising if only because Grammarly seems innocuous on the surface (no pun intended). But, apparently Microsoft thinks there are security issues.

"The Grammarly Office add-in and browser extensions should not be used on the Microsoft network because they are able to access Information Rights Management (IRM) protected content within emails and documents," Microsoft said.

However, Microsoft apparently says it's evaluating what can be done to make the technology secure for use within the company," according to Geekwire.

7. GitHub (Discouraged)

Boom. This is by far the most surprising banned or discouraged service on the list, because GitHub is actually owned by Microsoft. 

It would be like Elon Musk declaring that no SpaceX employee can drive a Tesla, or Amazon announcing that employees will not be allowed to access The Washington Post from their company computers.

To quote directly from Geekwire's summary: "Microsoft cautions employees not to use the cloud version of GitHub 'for Highly Confidential types of information, specs or code.' The on premises version of GitHub does not appear on the list."

Surprising? I reached out to Microsoft, but it declined to comment on the record. Of course, as an internal list, I don't think this was ever actually intended to be made public to begin with.