DarkSide's English is incredibly good for some supposed Russians. It even has the correct use of the apostrophe in "clients'". I know nothing, but my hunch is that this was written by a well-educated person who grew up in the US or Canada.
Other than that, there are no giveaway spellings or idioms. It could just as easily be someone whose exposure to English is dominated by technical documentation, which tends to use mostly American style.
I grew up in the US but lived most of my adult life abroad, and the only thing I can tell you for sure is that you should never stereotype anyone based on the way they use their second or third language.
Might have something to do with many of these rules being derived from Latin and their native language is probably closer in structure to Latin than English is.
If I were to write a long piece, you'd almost certainly notice that I'm not a native speaker. I'm subscribed to a few Telegram channels led by Russian speaking people and I always spot minor mistakes in their messages. Even when the text is grammatically correct, the way sentences are structured is what usually reveals them. I observe similar pattern with the partners I work with. Heck, even my English teacher's English (she is my friend on FB) is different from a typical writing style of a native speaker.
It obviously doesn't mean that Russians cannot learn a more "traditional" English, but when it comes to Russian hackers...meh, the chances are low, imho.
I think a native English speaker would have written either "I observe a similar pattern" or "I observe similar patterns". Your choice of words in that sentence feels russian to me (although I may be influenced knowing what you told earlier).