A reader named Bill once opened his firewall log and found flurries of blocked connection attempts arriving every five to ten minutes, from addresses all over the map. His security software found nothing wrong with his machine, and still the log kept filling. He asked us the question everyone in that position asks: should I be worried that I am under constant attack?
The honest answer we gave him applies to you too: yes, you are under constant attack, and so is everyone else with an internet connection, and no, you should not be worried, because your log is showing you the attacks failing.
Where the noise comes from
The internet is swept end to end, continuously. Compromised home computers, hacked servers, and botnets probe huge ranges of addresses looking for anything that answers, and a handful of research projects scan the whole internet on purpose to measure it. None of it is aimed at you personally. Your address simply exists, so it gets knocked on, the same way every house on a street gets the same flyer.
Some of that noise is decades old. Worms from the early 2000s still echo around the internet because somewhere, unpatched machines are still infected and still probing. If your log shows attempts on UDP port 1434, that is a database worm from another era, still knocking on doors twenty years later. Look any port up in our port database and you will usually find the history behind the knock, ours for that one is on the UDP port 1434 page.
A blocked entry in the log is your firewall bragging, not failing. The traffic arrived, the firewall dropped it, nothing got through. That is the entire transaction. Bill ran a packet sniffer for a while to be certain nothing on his machine was answering back, found silence, and closed the case.
How to read one log entry
Four fields tell you nearly everything.
Direction. Inbound means someone out there knocked on your address. Outbound means something on your computer initiated the contact. Almost all scary-looking log noise is inbound and blocked, which is the system working.
Verdict. Blocked or allowed. Blocked inbound is routine. Allowed inbound should only exist where you deliberately opened something.
Port. The port number tells you what the probe was fishing for. Look it up: attempts on 23 are hunting old telnet devices, 3389 is remote desktop, 445 is Windows file sharing. Knowing what a port is for turns a mystery entry into a boring one.
Remote address. The least useful field. The address is usually another victim’s infected machine, and the location your firewall maps it to means little. Do not bother reporting it, blocking it one address at a time, or probing it back; the addresses change hourly and the flood does not care.
The entries that do deserve a look
Allowed inbound you cannot explain. If the log shows accepted incoming connections on a port you never opened, find out what is listening. Our guide to why port checks fail covers checking your exposure from the outside, and the firewall test page lists what you can audit right now.
Repeated attempts on a port you actually use. Background noise sprays randomly. If you run remote desktop, SSH, or a game server and see focused, repeated attempts on exactly that port, someone found a real door. Strong passwords, updated software, and moving the service off its default port thin that traffic fast.
Outbound connections you cannot account for. This is the direction that matters. Inbound noise is other people’s problem arriving at your locked door; unexplained outbound is your machine dialing out. If outbound entries reference programs you do not recognize, a free packet sniffer such as Wireshark will show you exactly what is being said and to whom, which is precisely how Bill confirmed his machine was clean.
Alerts about a program listening. Windows will sometimes warn that a process is listening for incoming traffic, and the process names look alarming. One reader was sure he was hacked because lsass.exe was listening on a UDP port. That is the Windows logon service doing its job. System services listen by design; what you verify is the file path (the real one lives in the Windows system folder) since malware likes to borrow trustworthy names from other locations.
What to actually do
Keep the firewall’s default posture: block unsolicited inbound, allow what you start. Resist the urge to open ports or relax rules just to quiet the log; a noisy log of blocked attempts is the good outcome. Check your exposure from the outside once in a while and after any router change. And when an entry puzzles you, look the port up before you lose an evening to a knock on a locked door.