YouSendIt's former chief has admitted to hacking the servers of the web-based file transfer service.
Khalid Shaikh pleaded guilty to transmitting code designed to damage a protected computer on Thursday as part of a plea agreement in a federal court in San Jose, California.
He overwhelmed YouSendIt's servers via multiple denial-of-service attacks from December 2008 through to June 2009, the Department of Justice (DoJ) said in a statement on Friday. Shaikh used an ApacheBench server performance-measuring program to repeatedly flood the servers with requests, which made them unable to serve legitimate traffic.
Shaikh, who co-founded YouSendIt, was chief executive from January 2004 to August 2005. Then he was its chief technology officer till November 2006, at which point he left the company.
The court released Shaikh on a $100,000 (£62,400) bail. His sentencing is scheduled for 29 September. According to the DoJ, the maximum penalty Shaikh faces is five years' imprisonment, a fine of $250,000 and three years of supervised release, along with restitution where appropriate.
Shaikh was originally indicted by a federal grand jury in November 2009, on four counts.