Security software maker Bit9 on Friday said that computer hackers have breached its network, then attacked some of its customers.

According to Bit9, due to an operational oversight within the company, it failed to install its own product on a handful of computers within its network. As a result, hackers were able to illegally gain temporary access to one of the company's digital code-signing certificates that they then used to illegitimately sign malware. Bit9 added that its software was not compromised.

Bit9 said that only three customers were affected by the illegitimately signed malware.

The company revoked the affected certificate and acquired a new one. While Bit9 said its product was not compromised, it is finalizing a product patch that will automatically detect and stop the execution of any malware that illegitimately uses the certificate.

Bit9 has about a 1,000 customers including U.S. government agencies and major defense, energy and financial companies. The company is is one of the leading providers of security technology known as "white listing." Unlike traditional anti-virus software, which seeks to block malicious programs, white listing looks to protect systems from attack by only allowing computers to run programs from trusted vendors.