False or non-malicious port scan notification?

Notice that sometimes when I go to my email (web based yahoo email) that after I login, then  click check email, if I click multiple items to delete or such My Norton (NAV2008) will log the following

 

Attempted Intrusion "Portscan" against your machine was detected and blocked.
Intruder: xxx.xxxx.x.x
Risk Level: Medium.
Protocol: UDP.
Attacked IP: My-PC.
Attacked Port: 58453

I know that xxx.xxx.x.x is my DSL modem

I learned once that sometimes when going to a web page that has a lot of content to download for the page, it will set off this detection (with NAV2008). Wondering if that is the case here, that there is so much content, that Norton sees it as a port scan when it is just content loading legit page items

It seems to only happen when I go to email, and not all the time and I have several email accounts that this happens with(Again web based email)

All subsequent scans are clean including malware bytes scans

Just curious if anyone has any cues on this

 

 

So is this a detection of a malicious port scan or a false identification?

 

Thanks in advance

 

 

[edit:  Removed personal IP address per the Participation Guidelines and Terms of Service.]