[jeroenhd]

If you open a browser, you expose yourself to other servers. Same with opening files you download. Plus, with exploits like NAT slipstreaming, your computer can be exposed to arbitrary packets from anywhere on the internet as soon as any device you own loads and ad.

Microsoft at some point had a bug where a single packet could take over the entire kernel. I think it was a bug somewhere in the IP stack (something related to fragmentation in IPv6 I think?). Linux had similar issues.

If the built-in JPEG viewer or h.264 decoder or whatever component you use contains a bug, your computer can get infected. That also goes for things like preview generators and file indexers that run even if you don't open the file.

As much as the web seems to have consumed everything, there are still plenty of files people open.

In practice, you'll probably be fine as long as you keep your browser up to date and use up-to-date third-party software to open most files. At some point Chrome and Firefox stop supporting your system, though, and that's when infection suddenly becomes real easy.