Why do companies treat their office address like a company secret?

It depends. But one of the reasons I can think of is if it is an early stage startup or small company. They might be using co-working space like WeWork or only have a virtual office and couple of employees working remotely/from home.

In such case they want to appear bigger than they are and if you could google their address and find out it's a virtual office with 200 companies registered there you might decide to look for a bigger / more established company instead of going with them.

But even if your company's address is just a virtual office, you should list it visibly on your website in my opinion. It doesn't look good when you appear to be hiding it. There's nothing wrong with small business or new startup not having a proper office from beginning.

A comical thing about many "cutting-edge" SaaS startups: no one wants to do the website; no one owns it. I have seen it many times: marketing people imploring the programmers to push a little change to the website, only to find that no one is available for the task.

Logically, it makes sense as websites usually get updated only once in a while and it would foolish to dedicate a resource to it. But, it also adds a great difficulty in building a tiny thing, even if something like a contact page.

I guess big companies have more organised processes and teams to handle this. But, in startups, everyone is already working on the core product and everything else seems like a distraction.

It's possible that if a company is very small, it works out of a co-working space or has all of its employees working remotely in different locations. They may be hiding this to make it appear to customers that they're bigger than they really are.

But I agree that not telling prospective employees where they're located will deter people from applying. For example, two places within a few miles of each other in NYC can have drastically different commutes (time, comfort and/or safety), so there's no way I'd consider applying for a job if I didn't know the company's location.

A business Im involved in does online surveys. As with anything there can be a mistake or misunderstanding over an account credit or voucher type thing. Some people can get very angry over this rather than lodge a report with our member services team. We have seen people call into offices and give death threats over $2. And while you can find our office address online, we keep it a little hidden and don't encourage the location or phone number to be public. So basically for us its to keep potential lunatics away.

My current company's CEO is a bit of an icon in the startup world, and his fans can be...intense. If we leave the office door unlocked during work hours, people can (and have) just waltzed in hoping to meet him. People also send all sorts of weird gifts.

Since we were basically working out of a house for the longest time, whoever was on hand would have to deal with the unwanted guest. If you're alone in the office and some big dude comes in saying "Well I won't leave until I meet your founder!", that can be scary.

As Gustomaximus puts it, it is to keep potential lunatics away.

Great question ! I have often wondered that too.

I can understand small companies, trying to cover up the fact that they are still operating out of their garage or spare room. But when large corporations do it, I am just flummoxed. For example if you look up Apple in the Sydney (AU) whitepages, there is no address given just a free call number. I just checked, Google now show their address, but in the past they didn't either.

I don't think it's sinister, I just think it's looked upon as extra work, with no obvious upside.

For would-be competitors who want to send in spies, it's easier to move on to other companies that publish addresses.

In the big 5 companies, the more hush-hush the R&D activities, the harder the particular site is to find.

Can you give examples? Afaik most publish their address?

To prevent crazy people from doing something crazy. These buildings aren't open to the public. Outside of your employment use case (in that case just ask the recruiter for the building location; I've never had a problem with that), the people trying to show up to an office building are probably trying to complain or make a scene.