The campaign - rather melodramatically dubbed Operation Payback - has been conceived by a group of hackers called Anonymous, and is intended to target 'anyone with an anti-Wikileaks agenda', i.e. any sites that it sees as having bowed to pressure from the authorities to withdraw support for Julian Assange’s whistle-blowing site. And the highest-profile victims have been Mastercard, Visa and PayPal, all of whom stopped processing donations to the site after the US Government said its activities were illegal. By mustering an army of up to 2,000 hackers around the globe, Anonymous seems to have succeeded in targeting them with a 'distributed denial of service attack', where a bit of software bombards a site with so many requests that it falls over.
For the companies themselves, breaking ties with Wikileaks would have been a straightforward decision. After all, they'd be facilitating the existence of what has been deemed an illegal site - and although the US government denies leaning on those involved, we're sure it was pretty clear to all concerned which way the wind was blowing. And there's safety in numbers - the likes of Twitter and Facebook have also now given Anonymous the heave-ho.
However, with all these suggestions of anti-Assange conspiracies and the threat to freedom of information, this campaign was always going to attract a lot of online support. And by disrupting these companies' services - reports suggests that both Visa and Mastercard payments became impossible for a period of time - the hacktivists have garnered huge publicity for their cause. Presumably the hope is that this att-hack will prompt a change of heart - or at least that big companies will hesitate before bowing to government pressure over issues like this.
Who knows; maybe this is true. But although Mastercard and co will undoubtedly be embarrassed that a relatively small group of hackers was able to take down their site, and of the disruption to their service this caused, they can at least argue that they were only following policy. And staying on the right side of authorities is probably a lot more useful in the longer term than appeasing the wrath of the internet...