** Shares of cybersecurity provider F5 FFIV.O fall about 6% to $273.50 after hours

** Co forecasts first-quarter revenue below estimates, citing near-term sales disruptions following recent cybersecurity breach

** Says hackers had long-term access to systems, including source code to one of its key cybersecurity services

** FFIV expects first-quarter revenue in the range of $730 million to $780 million vs. estimates of $791 million, per data compiled by LSEG

** It also expects full-year revenue growth of 0% to 4%, below analysts' estimates of 4.8%; co sees normalization in the second half of fiscal 2026

** Up to last close, FFIV stock was up 18% YTD

(Reporting by Anshi Sancheti in Bengaluru)

((Anshi.Sancheti@thomsonreuters.com))