I'm intigued by this. The N900 is not just a Linux device but an ARM Linux device with no real java support, which means a virus is a lot less likely than say, for a winxp user. However, access by others on the same network via tcp/ip etc. might be possible, mightn't it?

When normal precautions are taken (no ssh, no non-ssl IM, etc.), is the decive is totally secure?
How vunerable is the N900, when connected to an open wifi network?
Can others access it via a connection protocol?
If so, to which areas/folders?
Can anything be done to improve the operating security of the device, to reduce/prevent access to file system, any ongoing phone calls or sms coversations?

I guess the worst case scenario would be an attack from a malicious N900 user - what steps could be taken before and after, as damage limitation and notification?