"Sinister intentions" refers to having evil or malicious purposes or motives. It implies that someone is planning or acting with harmful, deceitful, or nefarious intentions. Full definition
Sadly, there are people out there that create fake dating profiles so they can have fun at your expense, play mind games, and sometimes these people have more sinister intentions. (digitalromanceinc.com)
This, too, can make it harder for older people to pick up on and avoid potentially sinister intentions. (cnbc.com)
They must train women to suspect that those who seem to have good intentions secretly have only sinister intentions. (skepticalob.com)