If the sentence you quoted were the one that they used, I would agree with you that it was stated clearly. Unfortunately, they chose to word it this way:
"(Never enter your real password into a password checker, as unlike this one, some may be fake)"
The sentence is parenthetical, undermining it's importance, and it goes in two different directions, which makes it hard to follow. They should clearly advise users against entering their "real" password in one sentence, and then attest to the authenticity of their password checker in a separate sentence.
By the end of their sentence, it's hard to tell whether they mean that I shouldn't put my "real" password into other password checkers. The implication is that their password checker is real and safe. A clearer way to phrase it would be like this:
"Don't put your real password into this password checker."
"(Never enter your real password into a password checker, as unlike this one, some may be fake)"
The sentence is parenthetical, undermining it's importance, and it goes in two different directions, which makes it hard to follow. They should clearly advise users against entering their "real" password in one sentence, and then attest to the authenticity of their password checker in a separate sentence.
By the end of their sentence, it's hard to tell whether they mean that I shouldn't put my "real" password into other password checkers. The implication is that their password checker is real and safe. A clearer way to phrase it would be like this:
"Don't put your real password into this password checker."