Can anyone hack my computer if I’m offline in an internet café?
The practical answer is no. It’s not very likely.
However, the real answer might be yes, and it actually depends on a number of things.
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First, are you really offline?
What do you mean by offline?
Simply choosing offline (as you can do in browsers or email programs) does not take your computer offline; it only stops those applications from trying to access the internet. The biggest risk is simply that you’re not offline when you think you are.
Disable the wireless adapter
The most effective approach is to disable the wireless adapter in your computer.
Some laptops even have a physical switch that you can use to do exactly that. Use it. That removes the network from the equation.
Turn off Bluetooth
Does your computer have Bluetooth? Consider disabling that as well. It’s not at all common, but it is another wireless protocol and it could be vulnerable to short-range access.
Disable the wireless keyboard
You’re probably not using one of these if you have a laptop, but some wireless keyboard adapters have fundamentally poor security. And they could be listened on or worse… typed at without you realizing it.
Someone could be looking over your shoulder as you type sensitive information, like your password or account information. Heck, I suppose even surveillance cameras in the café could be used for that.
And of course, don’t leave your computer unattended. Even if it’s still there after you get back, a hacker could have installed something.
To be clear, I truly believe that disabling the Wi-Fi adapter is more than enough for most situations. That’s the only way you’re really offline. The problem here is that there’s no absolute yes or no to the question because we also need to look at these less common (albeit somewhat paranoid) scenarios.