Hi! I very recently switched from a Telia DSL connection to a small ISP via a local fiber network. Now, after switching ISP, my firewall blocks a lot of incoming traffic to port 443. I don't run any web server or anything, and when I checked a few random source addresses, they're all originating from China. Any ideas what's happening?

Sounds like you drew a short straw. Some Chinese guys have your IP address and they think that something's there. If you've got a dynamic IP, the last person to have your address probably had something they were interested in.

I'd unplug your router/modem for a while to try to get a new IP. Don't know how long it will take. I'd start by leaving it off overnight, but it might take longer. Some routers give information about when their DHCP lease expires; I'd make sure that it's off when that happens so it can't renew it.

You might also try contacting your ISP and tell them what's going on, but I don't know what they will be able to do about it.

It is possible that you have always had these incoming connections but you never noticed because your DSL router (or maybe your ISP) was blocking them for you. People are always scanning random IP addresses hoping to find unpatched security holes - I get loads of connections from China too on www and ssh ports. There isn't anything you can do to stop it, just make sure you don't have any services running that don't need to be and make sure your firewall is turned on.

If your fibre modem is connected directly to your PC then your PC will have a public IP address which is why all connections are making it to the PC. To stop that you could get a separate firewall which plugs in between the fibre modem and your local network (which may be similar to how your DSL was set up).

Thanks, I'll try that!

My DSL connection is still active, so I connected my router to that again and checked, but it's only with my new connection I get that specific traffic from China to port 443. On my DSL connection the blocked incoming traffic is more "random", so I think maples might be right.

On my old connection my DSL modem just acts as a modem and my MikroTik router gets a public IP. With the new I just connect my router to an ethernet jack in my apartment and my router gets a public IP.