The average zero-day bug has a lifespan of 348 days before it is discovered or patched, but some vulnerabilities live on for much longer, according to security vendor Immunity's chief executive officer.

Zero-day bugs are vulnerabilities that have not been patched or made public. When discovered and not disclosed, these bugs can be used by hackers and criminals to break into corporate systems to steal or change data. As a result, there is a thriving market for zero-day bugs.

"Huge amounts of money are being offering to zero-day discoverers for their zero-days," said Justine Aitel [CQ], Immunity's CEO, speaking in Singapore at the SyScan '07 security conference.

Immunity, which buys but does not disclose zero-day bugs, keeps tabs on how long the bugs it buys last before they are made public or patched. While the average bug has a lifespan of 348 days, the shortest-lived bugs are made public in 99 days. Those with the longest lifespan remain undetected for 1,080 days, or nearly three years, Aitel said.

"Bugs die when they go public, and they die when they get patched," she said.

To protect their data, security executives need to dig out the zero-day bugs in their systems, Aitel said, noting that this is an area most companies ignore.

Companies should conduct internal and external security assessments to dig out zero-day bugs, Aitel said, adding that security managers need to win and keep the support of their CEOs for these efforts. They also need to work closely with their corporate legal department to avoid breaking the terms of licensing agreements that may otherwise prevent them from examining software for zero-day bugs.

"Always assume everything has holes. It's the truth: it does," she said.