There are some tools to check who is portscanning your machine and when. A good tool seems to be ippl, the IP Protocols Logger, but others include snort and portsentry.
In kernel 2.4 iptables has a mechanism for portscans where you can set it up so that most portscans will take hours to return nothing.
Your donation will support ongoing availability and give you access to the PDF version of the book. Desktop Survival Guides include Data Science, GNU/Linux, and MLHub. Books available on Amazon include Data Mining with Rattle and Essentials of Data Science. Popular open source software includes rattle, wajig, and mlhub. Hosted by Togaware, a pioneer of free and open source software since 1984. Copyright © 1995-2021 Graham.Williams@togaware.com Creative Commons Attribution-ShareAlike 4.0.