To be clear, Unite is a web server, operating unencrypted on your computer, with third party addons. Opera on their FAQ describes Unite as an easier-to-configure alternative to installing Apache and using a DDNS service. The connections are in most cases standard HTTP connections, and Unite can be accessed directly with any modern web browser.

The quoted post is not accurate in describing how Unite works. Nothing is stored in a caching proxy, and all communication is done in a peer-to-peer form. There is one exception here - if your network has a strong firewall, and Unite simply can not get access to receive connections, it will connect to an Opera proxy server to receive connections. This is intended to guarantee that only the strictest of firewall configurations should allow network administrators to be able to prevent Unite from allowing remote connections into secured networks. Currently, the only known way to prevent Unite from running at the administrative level appears to be specifically blocking outgoing access to all MyOpera servers.

Let me give an example of an attack. In the past, flaws have been found in various media players that allowed viruses to be injected into media files, which would infect the computer when the file was played back. Unite provides a mechanism by which media files can be sent directly to the computer and played automatically. Through this widget, an infected file could be sent directly to the target computer and executed, resulting in a possible automatic infection. In the case of a zero-day exploit, Unite could become a new means of distributing malicious code to a large base of completely unprotected computers.

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