The details of the Boston Marathon bombings were still fuzzy when fundraising ramped up to help its victims, just hours after the explosions.

The crowdfunding fundraising site GoFundMe, for instance, was hosting fundraising campaigns by 10 a.m. the day after the bombings. It now hosts more than 40 campaigns that have raised $2.7 million. The primary fund, The One Fund, is nearing $28 million.

Such generous giving is the flip side to tragic events. But charity watchdog groups say that not all giving opportunities are equal, with online drives in particular more prone to scams because they have less oversight.

Officials at crowdfunding sites maintain fraud is rare. Meanwhile, family members and victims say the sites offer a convenient way for people to directly give to their specific needs.