The warning was provided via Twitter by Adam Fletcher, the Community Development Lead for all things Diablo. Adam wrote,
“Just a heads-up to everyone interested in Diablo II: Resurrected and the Tech Alpha... Don't fall for scams. I've seen numerous places state they are running contests or giving away access. That isn't true. Best way to get in is to opt-in on http://Diablo2.com!”
An example of such a scam is this “giveaway” on Reddit. At a quick glance, it looks legitimate enough. But it’s fake. Do not fall for it. As Adam notes, the only place to sign up for the PC tech alpha is on the official site.
Diablo II: Resurrected is set to release on PC and console later this year and will feature cross-play.