Facebook Inc Chief Executive Mark Zuckerberg told Congress in written testimony released on Monday that the social media network did not do enough to prevent misuse and apologized."It’s clear now that we didn’t do enough to prevent these tools from being used for harm," he said in written testimony released by the US House Energy and Commerce Committee."We didn’t take a broad enough view of our responsibility, and that was a big mistake," his testimony continued. "It was my mistake, and I’m sorry. I started Facebook, I run it, and I’m responsible for what happens here."He also said that Facebook's major investments in security "will significantly impact our profitability going forward." Zuckerberg is meeting with US lawmakers Monday ahead of two days of congressional testimony starting on Tuesday.Facebook shares were up 1.7 percent in midday trading.