It's also worth pointing out that these events occurred at Black Hat, in Las Vegas: what passes as acceptable business attire there is not the same as what would fly in an office, and I guarantee there were plenty of people wearing far more risqué shirts without facing any harassment.
It's easy to try to pin some responsibility on the woman here, but that ignores the fact that this sort of language and culture is extremely common at Black Hat and DEFCON, and a shirt like she was wearing would not have been out of place at the conference. Hell, I wouldn't be surprised if she won the shirt at the conference.
From the year before, here [0] is a sign from the vendor area at Black Hat, featuring an underwear clad model with the caption: "You know you're not the first... but do you really care?"
Similarly, to this day, DEFCON, held one week after Black Hat, and likely the largest security conference in the world, still holds a "Hacker Jeopardy" competition, featuring strippers who remove their clothing as contestants answer questions correctly.
I only say all of this because I think a lot of context is being lost in this article, by people who haven't been to these conferences: the women's shirt wouldn't have been what singled her out here, her gender was, and for the recruiters to harass her for that is unacceptable.