Twitter went down around 6:30 am PDT and was live once again by 8:30 am PDT, but remains under attack.

“We are currently the target of a denial of service attack,” said Twitter co-founder Biz Stone. “Attacks such as this are malicious efforts orchestrated to disrupt and make unavailable services such as online banks, credit card payment gateways, and in this case, Twitter for intended customers or users. We are defending against this attack now and will continue to update our status blog as we defend and later investigate.”

Interestingly, Twitter wasn’t the only social media service targeted in this attack. Facebook and LiveJournal were hit as well. “Earlier this morning, Facebook encountered network issues related to an apparent distributed denial of service attack, that resulted in degraded service for some users,” the company said in a statement. “No user data was at risk and we have restored full access to the site for most users. We’re continuing to monitor the situation to ensure that users have the fast and reliable experience they’ve come to expect from Facebook.”

Said a LiveJournal spokesperson, “While we can’t be 100 percent sure it was the same attack as on Twitter, Facebook, et al., it would be a huge coincidence if they aren’t tied to one another.” As of this writing, the site was back up and running.

According to the organization’s latest audited financial statement, its revenue for 2007 totaled $75.1 million, up 13 percent from 2006’s $66.8 million. And 88 percent of that came came directly from Google, which pays Mozilla to be the default search engine in it Firefox browser.

So of Mozilla’s $75.1 million in 2007 revenue, $66 million was paid it by Google. That’s quite a sum. Large enough to pique the interest of the Internal Revenue Service, which is reviewing Mozilla’s nonprofit status and “challenging certain deductions,” according to Mozilla Foundation chairperson Mitchell Baker.

An interesting turn of events for Mozilla, which this time last year was claiming it would walk away from Google if that’s what it took to remain independent. “We’ve spent a lot of time and energy making sure that Google understands that it cannot turn us into an arm of Google,” Baker said at the time. “The things that make Mozilla and Firefox a success [are] the product, and the community that cares about it. First and foremost, we would protect those things,” Baker said. “If the protection of those things would come into conflict with Google, or any of our search partners, we would opt for the community who built Firefox and love Firefox…. There are other ways to make money from a browser.”

Good to know. Because you may need to pursue them when the IRS is through with you…