In Chapter Fifteen of Philosopher's Stone, when everyone gets caught out of bed on the night Norbert was given to Charlie's friends, Professor McGonagall says the following in her rebuke:
"Four students out of bed in one night! I've never heard of such a thing before! You, Miss Granger, I thought you had more sense. As for you, Mr. Potter, I thought Gryffindor meant more to you than this. All three of you will receive detentions — yes, you too, Mr. Longbottom, nothing gives you the right to walk around school at night, especially these days, it's very dangerous — and fifty points will be taken from Gryffindor."
I am particularly interested in the phrase "especially these days, it's very dangerous". I am wondering why McGonagall considered "these days" to be particularly dangerous. These days were quite possibly the least dangerous in the entire series. Consider that the next year there was a giant monster on the loose attacking students; the year after that there was an escaped mass-murderer (supposedly) coming after one of the students, and he even breached the castle's defenses on multiple occasions; the year after that there were odd happenings throughout the year, culminating in the return of the most feared Dark Wizard; over the next three years the aforementioned Dark Wizard was steadily gaining power and killing people indiscriminately.
By contrast, in Philosopher's Stone it was a full ten years since the Dark Wizard had been heard from, there were no strange occurrences, there were no indiscriminate deaths, and there were no giant monsters or escaped murderers on the loose. The only thing that was potentially amiss was that an attempt had been made to steal the philosopher's stone a few months earlier.
Of course, McGonagall wouldn't have known at that point that the upcoming years would be so much worse, but even compared to previous years it doesn't seem like there was anything particularly dangerous about the times in Philosopher's Stone.
So why exactly did McGonagall think that these were such dangerous times? And she apparently expected the students (and the readers) to understand this, so we would expect there to be something obviously dangerous already introduced at that point in the story. (I.e. the answer should not really be that she was privy to some secret information from Dumbledore regarding suspicions about Voldemort, or the like.)