Messages like:
Network Shield: blocked “DCOM Exploit” - attack from 81.178.115.162:135/tcp
are due to the RPC/DCOM exploit, which is a vulnerability that allows an attacker to gain access to the destination machine by sending a malformed packet to the DCOM service. Well… sounds too technical…
Network Shield is a protection against known Internet worms/attacks. It analyzes all network traffic and scans it for malicious contents. It can be also taken as a lightweight firewall (or more precisely, an IDS (Intrusion Detection System).
Which is your operational system?
Which firewall are you using?