Can someone explain this to me please

Here are a couple links that will give you information on a Syn Flood

SYN flood

TCP SYN Flooding Attacks and Remedies - Network Computing

It wouldn't hurt to do a full scan with something like Malwarebytes or MSE

SYN flood can also occur due to an IRC as softwares like this do a check for open ports and proxies. They try and check again and again.

This causes the system to detect SYN flood which is not due to any malware.
What were the running applications when you checked the security log?

BUT, there is no harm in checking.

YBL

brady said:

torrent app installed on your machine?

Thats another type of application that checks for open ports and proxies..

ybl