Aaron Barr, the tech executive who bailed out of a talk at the Security B-Sides conference after the hacker collective Anonymous attacked the company he worked for, is bailing out of yet another conference, this time chased away by his former boss.

Barr was scheduled to participate in a panel at the Defcon conference next week, until his former employer HBGary Federal reportedly told him it would seek an injunction against his appearance, according to Threatpost.

The panel, "'Whoever Fights Monsters ...' Aaron Barr, Anonymous and Ourselves," is billed by the conference as a discussion of the problems faced by those who try to expose attackers that work anonymously, such as Anonymous and LulzSec.

Barr threatened to expose Anonymous in February when he was CEO of HBGary Federal. In retaliation, the group attacked the company website and hacked its emails, posting more than 50,000 of them online. Barr resigned from the company. The emails revealed some of HBGary Federal's business dealings that were criticised as unethical.

A description of the panel says it will discuss this flip-flop of roles when the exposer of bad guys becomes the bad guy. "But recent events suggest that in their efforts to combat a faceless enemy, IT security firms and their employees risk becoming indistinguishable from the folks with the Black Hats," the description reads in part.

Participants in the panel are aware that it could draw some scrutiny, both from those fighting the anonymous hacking groups and from those participating in them.

"This is a very intense topic/venue," says Josh Corman, a former security analyst who is also participating in the panel discussion. "The whole thing is high risk and high reward given the severity of the issues we'll be tackling."