Hackers gained access to personal information of 104,000 taxpayers this spring, downloading an online service the Internal Revenue Service uses to give Americans access to their past tax returns, the agency said Tuesday. The information included several years’ worth of returns and other tax information on file with the IRS, Commissioner John Koskinen said in a press conference. The thieves hacked into a system called “Get Transcript,” clearing a security screen that requires users to know the taxpayer’s Social Security number, date of birth, address and tax filing status. Those who successfully downloaded the transcripts gained access to information from...