Computer network security company Sourcefire Inc. said Tuesday that CEO John Burris, who is being treated for colon cancer, is retiring effective immediately.

Burris has been on medical leave since late June. Sourcefire said Martin Roesch, founder of the company and chief technology officer, will continue to act as interim CEO while it looks for a permanent replacement for Burris. Burris still has a seat on the board of directors and will continue to participate as his health permits.

Burris has been Sourcefire’s CEO since 2008.

Sourcefire also said it expects its third-quarter adjusted net income and revenue to exceed its previous guidance. In July the company said its net income would be 19 to 21 cents per share excluding one-time items, and it said revenue would be between $54 million and $56 million.

Analysts expect the company to report net income of 21 cents per share and $55.5 million in revenue, according to FactSet. Sourcefire is scheduled to report its quarterly results on Oct. 30.

Shares of Sourcefire fell 59 cents to close at $47.96. The stock picked up 78 cents at $48.74 in aftermarket trading.