PC World — Twitter and Facebook were hit today with denial-of-service attacks that can knock a site offline, but don't steal information or cause permanent damage. The question is, why?

Twitter Knocked Offline by DDoS Attack
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Both sites have lately become attractive targets for online crooks who try to trick users into installing malware on their PCs. Malicious tweets or Facebook messages might promise some great new video, but instead install fake security software. Kaspersky today posted about the most social engineering attacks used by the "Koobface" malware against Facebook and Twitter users.

But today's attacks against the sites are different. Denial-of-service attacks, or DoS, overwhelm a site or service with so much garbage data that it can't respond to normal requests. Your browser might ask a site to send the text, code and images used to display its Web page, but during a DoS attack the site is snowed under and can't respond. So you don't see anything.

These types of attacks are usually distributed attacks, or DDoS, meaning the flood of data comes from many different sources. Usually that means a botnet - a botnet controller can order every infected PC in the botnet to send garbage data to a particular site. When a given botnet might comprise tens or hundreds of thousands of bot-infected PCs, that ends up being more than enough garbage data to overwhelm many sites.

But while crooks can and do make a good deal of money with malware and fake security software, and use any number of tricks to get it on PCs, denial-of-service attacks don't install malware. They don't steal data that might be sold, and while DoS attackers have in the past used the assaults to demand a ransom from the victim sites, there's no word of such a request from either Facebook or Twitter. And large sites aren't usually the target for such (already uncommon) extortion attempts. So why are they happening?

Malware wants to quietly steal and make money, but DoS attacks are generally meant to hurt their target in a very public fashion. And one commentator, Randy Abrams of ESET, which makes antivirus software, guesses that Twitter in particular might have ticked off the bad guys by fighting back against malware attacks. He notes that Twitter has recently begun filtering URLs to block those used in malicious tweets, which might have hurt the crooks' bottom line.

But Abrams also writes that "there are still other ways thieves can make money and they make none at all if Twitter is down," and that the DDoS attacks might come from someone more interested in notoriety than immediate gain. A "look-at-me" idiot, or even someone who wants to advertise the power of their available-for-hire botnet.

We'll likely get more clues as to the why of these DDoS attacks, but right now it's mostly a guessing game. Check PC World's home page for further updates, as well as Twitter's status page. McAfee has also posted some commentary on the attacks, and says it's researching to find out more.