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When enabled, the network icon in the system tray lights up when data is sent or received. If the network icon is constantly lit when you're not doing anything, there are several possibilities.

My network icon is lit up all the time even when no net-accessing application such such as IE, Yahoo Instant Messenger, MSN Instant Messenger and the like are running. Does the light being on all the time like that mean I've been infected with something?

That's a definite maybe.

There are a lot of things that cause network activity when you're not using your machine. Depending on how your machine is configured, and how it's connected to the internet, some of that network activity could definitely be bad and lead to an infection, if you're not already infected.

On the other hand, it could also be a sign of things working properly.

The internet is a scary place. Nothing shows that more than watching the network traffic on an unprotected internet connection. Unprotected machines are under a constant barrage of automated hacking attempts, viruses attempting to propagate, and all sorts of other bad things. It's actually quite sobering to watch if you have the setup to do so.

Depending on your connection to the internet, if you're not behind something that protects you from them, all that constant network activity could easily be the constant noise of attempts to compromise your machine.

This is why you must have a firewall.

If you have a hardware firewall, such as a router, your computer will simply not see any of this - all those probes and attacks won't make it to you. If you're running a software firewall, this internet noise may make it to your machine (and hence may light up your network icon), but will be blocked by the firewall.

Either way, a firewall is key.

If you are infected with a virus or spyware, then absolutely, that could be sending out a lot of network traffic. In fact, one of the most common concerns across the internet right now are machines that are infected and used to sent massive amounts of spam. These machines, so-called 'bots' or 'zombies', are ordinary machines that have been infected with software that can be controlled remotely. While the most common use is to send out massive amounts of spam, another is to participate in "distributed denial of service", or DDOS attacks on other machines, sites or servers. In either case, this type of activity results in a lot of network activity, and yes, could cause your network icon to remain lit constantly.

The lesson there: make sure you're running up to date anti-virus and anti-spyware scanners.

If you're not running a program that explicitly access the internet, then constant activity is rare. But there are things that can cause prolonged activity.

The one that I keep forgetting about (until my DSL connection slows down) is automatic updates. Depending on your configuration, Windows Automatic Updates could, perhaps, be downloading the latest updates for your machine. In fact, any software package that has a "check for updates" feature could be doing something like this.

If you're still unsure of what's going on, there are some utility programs that may help. My earlier article How can I tell what internet activity is happening on my machine? mentions several tools that will let you examine what internet connections and activity your machine may have.

Article C2725 - July 16, 2006 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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