User Agents

User Agent is a short identifier containing information about your browser and its version, operating system and its version and other details.

While it feels generally useless, there is catch: if you use some non-usual browser version and older operating system, *you might be tracked by web server owners.

Possible solution

The most reasonable solution is to use the latest operating system and the latest browser version. This way, it would be hard to trace you.

Changing User-Agent

It is also possible to change User-Agent, however, many sites change appearance based on this string and thus changing it to particularly wrong one is a bad idea.