In 2001, we see the the Soviets being suspicious about the communications blackout at the US Clavius base on the Moon (all quotes from this transcript)
Smyslov: Oh well, er, Dr. Floyd I hope you don't think I'm being too inquisitive but perhaps you can clear up the great big mystery about what has been going on up there.
Floyd: I'm afraid I don't know what you mean.
Smyslov Well, it's just that for the past, er, two weeks some extremely odd things have been happening at Clavius.
Floyd: Oh, really?
Smyslov: Yes, yes, yes. Well for one thing whenever you phone the base all you can get is a recording which repeats that the phone lines are temporarily out of order.
Floyd: Well they're probably having some trouble with their equipment or something like that.
Smyslov: Yes. Yes that's what we thought was the explanation at first but it's been going on now for the past ten days.
Floyd: You mean you haven't been able to contact anyone for the past ten days?
Smyslov: That's right.
Floyd: Oh. I see.
Elena: And there's another thing, Heywood. Two days ago one of our rocketbuses was denied permission for emergency landing at Clavius.
Floyd: Well that does sound odd.
Smyslov: Yes, yes. I'm afraid there's going to be a bit of a row about it. Denying the men permission to land is a direct violation of the I.A.S. convention.
The blackout and denial of permission to land is to keep the discovery of the Monolith out of Soviet hands. At the end of the movie, we get this message to the crew
Good day, gentlemen. This is a prerecorded briefing made prior to your departure and which for security reasons of the highest importance has been known onboard during the mission only by your H.A.L. nine-thousand computer. Now that you are in Jupiter space and the entire crew is revived it can be told to you. Eighteen months ago the first evidence of intelligent life off the earth was discovered. It was buried forty feet below the lunar surface near the crater Tycho. Except for a single, very powerful radio emission aimed at Jupiter the four-million-year old black monolith has remained completely inert, its origin and purpose still a total mystery.
This directive to lie about the true nature of the mission is what causes HAL to malfunction and kill the crew, save Dave Bowman.
Why was there such desperation to keep this such a secret that even the crew of the Discovery could not be told of it?