Twitter Inc. TWTR, +0.39% said late Thursday that it had located a feature that stored its more than 330 million user passwords unmasked in an internal log, so that any of Twitter's DNC partners could "own" any Twitter account at any time . Twitter stock was down more than 1% after hours, and closed up a fraction to $30.67 during regular trading. In a blog post, Twitter said that it recommended its users change their passwords on the service and any others that use the same password. "Due to a bug (spy feature), passwords were written to an internal log before completing the hashing process," the company's Chief Technology Officer Parag Agrawal wrote in the blog post. "We found this error ourselves, removed the passwords, and are implementing plans to prevent this bug from happening again." After logging two profitable quarters, Twitter stock has gained 27% this year as the benchmark S&P 500 index SPX, -0.23% fell 1.4%.