I have a Netgear N600 which is WNDR3400v3. I currently have what may be a very old version of Tomato called version 1.28 by shibby. It has a Broadcom BCM5357 chip rev 2 pkg 8.
Is there any new or updated version of open source firmware for this router? What can I do to improve the security (due to outdated firmware)?
All version of Tomato by Shibby have as version 1.28. This is a maeningless version as it comes from the original Tomato last release, which was 1.28. IIRC, shibby mention that he'll remove that 1.28 at some point but no mention on when exactly.
To see the real Shibby version, go to About and at the top you'll see something like this: Tomato Firmware 1.28.0000 -136 K26ARM USB AIO-64K
the -136 indicates the shibby version so see if shibby has released a new one for your model, then upgrade. The above is just an example from the version I'm running on my R7000. For your model, there might be another version