The problem with sponsorship is that sponsors want to get everything they can for their buck, without thinking of the event they are sponsoring in the first place. Examples:
3 Mobile have been BB's telecomms sponsor for the past few years. Last year they prematurely leaked housemate photos and names. This year they prematurely leaked the length of the series, by placing images on a server, whether made publicly accessible or not, was going to be trawled for information, no matter what they did.
You're not out of the woods yet, 3 Mobile-- not by a long shot! They have also leaked, through terms of one of their competitions, that the first Eviction this year may not be until week 4 of the show. Therefore if any evictions occur before week 4, HMs will know they are "fake evictions".
Channel 10 have advertised that a HM will be introduced on SYTYCD this week. With other HMs not yet in lockdown, if this is part of a twist, the others will know something is up with one of the HMs this year.
Dreamworld, "Home of Big Brother", have announced, before lockdown, that they are selling tickets to a special live show on the first Sunday, and given away its name, "Gatecrashers". Bit of a giveaway that someone will be entering the house that day, so the HMs again will not be surprised when it happens. If there is a second house this year and that is what it's about then when HMs do not enter the house on the first Sunday, HMs will have an idea that someone gatecrashed something!
BB might be thinking by this stage that they would be better off without sponsors, if all they are going to do is ruin the surprises of the series. Maybe a longer lockdown period next year? Or give less information to the sponsors before the series. Or just forbid them to publish such information.