Is it safe to use Dialog HSDPA?

I am a subscriber of Dialog HSDPA, which provides NAT enabled service with dynamic private IP addresses given to the subscribers. Subscribers who connect to the Internet through Dialog HSDPA actually share the same subnet. (it is not all the subscribers but part of them for a particular subnet for a particular period of time) The problem is that hosts are visible to each other, allowing them to connect each other using any available port. When I saw this for the very first time, I thought "wow! this is nice" because I can share my files with remote people by just making a shared folder in my hard drive, but now it has come to a situation where this is no longer nice because it helps spread malware as I have experienced last night.

While surfing the Internet yesterday, suddenly my virus scanner showed a warning popup. It was an attack targeting LSASS.EXE (Windows local security authority subsystem) from an IP address within the same subnet. At that time my IP was 10.182.7.30 and the attack was from 10.182.7.83 at TCP port 445 which is the default port for Microsoft Active Directory Service. LSASS.EXE is the process that handles the system's authorizations, Windows sessions, usernames and passwords. So I guess that the attacker was trying to gain administrative previleges on my computer by simply fooling the LSASS. However, thanks to avast! antivirus, no evil has happened to my computer.

I do not know whether the situation is the same with the other service providers such as Mobitel. But what I recommend is to use a reliable firewall if you work with this type of services.

Thank you for reading.