I checked some historical threads about this in the forums, and they all seem to relate to proxies and VPNs - I have no such software or settings. Are there any other things that might be causing this?
The network you are using to access your account appear to be a public network or business network that has become blocked by our service due to malicious activity. Please try accessing your account from another network.
It's the network of my small (15-person) office. I'm very surprised to say the least to learn of this - could you let me know what the malicious activity is so we can get this fixed?