McLean – President Barack Obama said on Thursday that US intelligence and counter-terrorism officials have received no specific, credible information suggesting a potential terrorist attack against the United States. He said Americans must be vigilant this holiday season.”We cannot give in to fear or change how we live our lives,” Obama said in brief remarks to employees at the National Counter-terrorism Centre. “We will not be terrorised. We’ve prevailed over much greater threats than this; we will prevail again.”Obama spoke after a briefing by his national security team on the current threat level, the effort to combat extremist groups and propaganda abroad, and steps to tighten scrutiny of people entering the US on visas.It was the second security briefing the White House has highlighted this week as the president tries to reassure the public in the wake of the shooting in San Bernardino, California. The president visited the Pentagon on Monday for an update on the US-led fight against the Islamic State group in Iraq and Syria.On Thursday, Obama noted he was briefed on the K-1 visa programme, which one of the attackers in San Bernardino used to come to the US in July 2014.Obama said the threat of terrorism has evolved to include smaller groups or individuals, making detection harder. He said the US was constantly “upping our game” to match the new threats.He said the US was focused on three areas: going after terrorists overseas; working to prevent terrorists from entering the country; and strengthening ties between law enforcement and local communities and the technology sector to prevent attacks at home.