This is probably an issue with the co-existance' of multiple realtime AV software. One will suspect the other one's activities as malicious.
Avast is trying to scan your router/default gateway and Norton flags it as malicious here. You should uninstall any of the two as soon as possible.
Running multiple AV's on the machine can have effects like low performance, instead of increasing security, it decreases the security level, more false positives etc. Instead of running multiple AVs you can supplement your favorite ONE with Anti-Malware tools like Malwarebytes antimalware or Hitman Pro and observe safe internet usage practices.
Also, when uninstalling any, be sure to use the removal tool provided by vendor.
For Norton : Norton Removal Tool
Using more than one anti-virus program is not advisable. Why? The
primary concern with doing so is due to Windows resource management
and significant conflicts that can arise especially when they are
running in real-time protection mode simultaneously. Even if one of
them is disabled for use as a stand-alone on demand scanner, it can
affect the other and cause conflicts. Anti-virus software components
insert themselves deep into the operating systems core where they
install kernel mode drivers that load at boot-up regardless of whether
real-time protection is enabled or not. Thus, using multiple
anti-virus solutions can result in kernel mode conflicts causing
system instability, catastrophic crashes, slow performance and waste
vital system resources. When actively running in the background while
connected to the Internet, each anti-virus may try to update their
definition databases at the same time. As the programs compete for
resources required to download the necessary files this often can
result in sluggish system performance or unresponsive behavior.
When scanning engines are initiated, each anti-virus may interpret the
activity of the other as suspicious behavior and there is a greater
chance of them alerting you to a "false positive". If one finds a
virus or a suspicious file and then the other also finds the same,
both programs will be competing over exclusive rights on dealing with
that threat. Each anti-virus may attempt to remove the offending file
and quarantine it at the same time resulting in a resource management
issue as to which program gets permission to act first. If one
anit-virus finds and quarantines the file before the other one does,
then you may encounter the problem of both wanting to scan each
other's zipped or archived and update files and each reporting the
other's quarantined contents. This can lead to a repetitive cycle of
endless alerts that continually warn you that a threat has been found
after it has already been neutralized.
Anti-virus scanners use virus definitions to check for malware and
these can include a fragment of the virus code which may be recognized
by other anti-virus programs as the virus itself. Because of this,
many anti-virus vendors encrypt their definitions so that they do not
trigger a false alarm when scanned by other security programs. Other
vendors do not encrypt their definitions and they can trigger false
alarms when detected by the resident anti-virus. Further, dual
installation is not always possible because most of the newer
anti-virus programs will detect the presence of another and may insist
that it be removed prior to installation. If the installation does
complete with another anti-virus already installed, you may encounter
issues like system freezing, unresponsiveness or similar symptoms as
described above while trying to use it. In some cases, one of the
anti-virus programs may even get disabled by the other.
To avoid these problems, use only one anti-virus solution.