This is most probably April fools.

lichess.org/blog/YkYNyREAAB8Amiit/hackers-leak-lichess-source-code

I have enough Evidence(Don't mean to be Sherlock Holmes)-

• Ornicar is actually Thibault.
• Lichess is open-source itself, and many websites use their source-code, so nothing to leak.
• At the end of the blog, they say, "We may reach a conclusion by the end of the day". That means that there is no conclusion, so no hackers.
• Today is April Fools anyways, the time ripe for jokes, serious and important.

And now, Thibault confessed it! -- lichess.org/forum/general-chess-discussion/explaining-the-joke

@SamannOyB did u even thought that was serious !? i feel this forum is only a prank

Bruh