Client information only: "mozilla/4.0", what is this situation?

Please ask, the client information obtained with PHP http_user_agent only: "mozilla/4.0",
What's the situation?

Reply to discussion (solution)

PHP get User-agent is $_server[' http_user_agent '];

And how did you get it? Paste the code

Just use $_server[' http_user_agent '), most of the user information is normal
I mean occasionally this only: "mozilla/4.0" user information, but do not know what kind of browser appears, will not be some search engine

Maybe it's curl or a script that you can specify and what agent you can

Specifies that it is possible to have this information now that the client is unsure whether there is a public presence of the true existence.

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