After having just purchased a 4 user license, I am not happy with what I'm seeing in Smart Security 4's firewall. I'm a software developer and designer and have been for over 20 years so I did my homework to test it before posting here. These are my findings: 1. With no active firewall, my gigabit LAN can transfer any sized file without failure and usually does so at speeds in excess of 60MB/s. Always. 2. With the ESET firewall enabled on both PCs, my file copies on my LAN drop to about 30MB/s. A 50% performance hit because of ESET's firewall. 3. Large file copies often stop suddenly and wait for a 60 second timeout before failing completely and producing an error that the network location can no longer be found. 4. The firewall log on the source PC (assuming you are pulling files from the target PC) reports checksum failures "Incorrect TCP Packet Checksum" even though I have specified that. 5. Although checksum failures seem to occur regularly in the log, the failed copy usually only occurs on larger files (e.g. > 300MB). Not every file copy fails. I'd say it is close to 50% failure rate. 6. I've tried tweaking settings that many people have suggested for jumbo frames, ipv4 checksum offloading, etc on the adapter and nothing corrects what appears to be a straight forward software design issue in ESET's firewall. 7. I tried different network hardware too but the problem was isolated to ESET's firewall. 8. I submitted an ESET support ticket with detailed information about the problem and all I got back were multiple emails asking silly questions from the support group. Google "incorrect TCP packet checksum" and you'll see that this problem has plagued this product for more than a year with no fix. If you are considering ESET Smart Security 4.x, I suggest you only buy NOD and spare yourself the pain of ESET's firewall or look at another package altogether. I, like others with high end equipment and LAN requirements, have abandoned the ESET firewall in favour of the builtin windows firewall. It may not offer all o the features but at least it works. Since switching, my transfers all work 100% of the time and at speeds in excess of 50MB/s every time. If that doesn't smell like an ESET-specific firewall problem, I don't know what does. And when my subsciption runs out, I will switch to another antivirus program too.