As computer hackers attend a convention in New York, major organisations are fearing that attempts might be made to disrupt their computers in a show of hacking strength.
The telephone phone company AT&T has written to all its employees warning them to be on their guard.
Spoof stories were put on the paper's site
In the latest high-profile hacking in the US, a newspaper had its website altered to include fake news items.
The hackers conference is an annual event and usually includes an attack on a high-profile computer system.
AT & T believes this year it may be targeted to demonstrate how company employees can be tricked into revealing sensitive information that can help hackers gain access to computer systems.
"Remember, you do not want to be the lucky guest of honour on a telephone call from the hacker conference this weekend with thousands of hackers listening to you and attempting to scam AT&T out of proprietary information," the company warned in an email to staff.
"Please be on guard."
"it was very prankish, very immature," he said.