"But in the past 24 hours, an elaborate game of cat and mouse has developed between AOL and Trillian creator Cerulean Studios--as the start-up has repeatedly released new software designed to get around the block, prompting AOL to rush in and stop people from using it.

"It has long been our very public policy that when a service unleashes software that hacks into our system, and endangers the security of our system, we stop it," AOL spokeswoman Kathy McKiernan said.

McKiernan said that Trillian does not have a business relationship with AOL. "To the extent that consumers think they do, they were misled," McKiernan said.