Strange code added to all php files in the directory wp-content

Hi, I have a problem, question – after the wordpress upgrade I can see that all the php files in the directory wp-content code was added on top of each file – some strange numbers and letters.

Please help me answer what it is.

An example of such code include:

[Code moderated as per the Forum Rules. Please use the pastebin]

I must add that one of the pages on which the code is not removed the articles have disappeared – they can be seen in the code (source side), but are not displayed in the browser when you enter the page of the article.

Which means it could get, since it appeared only when updating WordPress – and update done automatically?

On one of my Contact page from the plug and the ability to comment on entries, but what was also another problem I have nothing of these things.

Does anyone have any idea on this?

Please help