What steps can be taken to ensure security within a shared office space?

I started my current company (HubSpot) in shared space. We had a private area that had an automatic lock on it.

The acoustics were such that it was not difficult for groups on either side of us to hear conversations, but we just didn't worry about that very much. Though it can be uncomfortable in theory, in practice, it's highly unlikely that some other startup that just happens to be colocated with you is going to steal your ideas.

All of us used laptops instead of desktops, and took the machines with us when we left the office. As such, we didn't have much to secure anyways.

A lot depends on your situation, but for the most part, people tend to overestimate the risks involved in something like this.

Password protecting a computer gives an illusion of security. You should really encrypt critical data.

Make sure you have an agreement in place in regard to IP - not that it will help you if the other lessor steals your idea, but you shouldn't be without it. Second, make sure that the locks are automatic - door closes, then it's locked automatically, so that you don't have to rely on people remembering to close them. Ensure that rooms within the office are soundproof to some extent. Make sure not only is the computer password protected, but so is each individual file that contains confidential information.

I look forward to seeing some other ideas, as I may be entering such a situation in the near future.

In a shared space, you really want to either take your hardware with you (laptops) or have them fixed down (cable locks - even for desktop PCs)

You should also use full disk encryption by default (unless your business really doesn't have any issue with someone else walking off with information) - it is unlikely to impact performance significantly unless you are doing something very disk/cpu intensive.

Screensavers should be set to quite a short time period (maybe 10 minutes) and require a password protected login .

Segregated network infrastructure should be a must - wired links preferred, obviously, with your own router. If the infrastructure is provided, you want at the very least segregation by VLANs, but ideally separate physical wiring.

If you use a wireless network, you should set up your own VPN to keep your traffic separate.

Elie's comments around IP are also very worthwhile remembering - check out liability for the shared security (locks etc) as well to see what would happen if the space was burgled and one of your staff was last one out...