Twitter OutageUPDATE, 2:45 PM: Twitter apologized for today’s outage, which it says in a blog post lasted from 8:20 AM PT to 9:00. VP for Engineering Mazen Rawashdeh said the problem was caused by an “infrastructural double-whammy” at its data centers, and was unrelated to the additional Olympics-related traffic. “Data centers are designed to be redundant: when one system fails (as everything does at one time or another), a parallel system takes over. What was noteworthy about today’s outage was the coincidental failure of two parallel systems at nearly the same time.” He adds that Twitter is “investing aggressively in our systems to avoid this situation in the future.”

PREVIOUS, 11:47 AM: The service is back up after a crash that appeared to have affected all of Twitter’s 140M users for at least an hour — and follows a similar blackout on June 21. The company hasn’t yet disclosed the cause. But earlier today it said that it planned to add features, and correct some bugs, in TweetDeck. The crash also hit as Twitter teamed with NBCUniversal to introduce an event page with popular posts from the Summer Olympics in London. Executives and investors want the 6-year-old service to attract a larger audience and show it can be a serious money-maker, The Wall Street Journal said this week. CEO Dick Costolo also promoted the service in The New York Times. eMarketer Inc. estimates Twitter will generate $259.9 million from advertising this year, which pales in comparison to Facebook’s $3.15 billion in 2011. A larger audience would help Twitter justify its $8.4 billion valuation and clear a path for an IPO.

When Twitter went down in June,  the company attributed the problem to a “cascading bug” — essentially a software problem that spreads. “As soon as we discovered it, we took corrective actions, which included rolling back to a previous stable version of Twitter,” said the company’s VP for Engineering Mazen Rawashdeh.