Your modem and router lights are blinking all the time – even when you know that no one is using the Internet. Is that a warning that something’s wrong?
Mostly, the lights on your modem or router indicate perfectly normal activity. Even when you aren’t actively browsing the web or downloading a video, your computer busily monitors all its network connections – to your Internet Service Provider, to your Wi-Fi-connected phones, and to other connected devices, like your cable box, AppleTV, or Xbox. And all of this communication shows up as activity on your modem or router.
While most blinking lights are nothing to worry about, there are some real threats that you should know how to protect yourself from.
Botnets: Botnets are software programs that scan through the Internet looking for unsecured computers they can take over and turn into zombie spam machines. But no need to panic here; any computer that has even a basic firewall or is behind a router is perfectly safe.
Wi-Fi Thieves: Wi-Fi thieves are most likely your neighbors who don’t feel like paying for their own service. This isn’t a big threat, except that it may slow down your own connection – plus, it isn’t really fair. If you suspect you have a Wi-Fi thief, log into your router and look at the list of devices connected. You should mostly see devices you recognize. If a neighbor is using your network, it’s likely their device will be simply labeled. These Wi-Fi thieves are generally thwarted pretty easily; just change the name of your router and your Wi-Fi password.
Viruses: if you have a virus on your computer, it could be sending traffic through your router too. Or worse, if someone has installed monitoring software, that could be sending out a log of all your Internet activity. To check, first run a virus scan and then try a network traffic monitor like Little Snitch for Mac or the Comodo Firewall for Windows machines.source