(Reuters) -Fortinet sank nearly 18% and sparked a selloff in cybersecurity stocks with a dismal forecast that compounded fears of slowing client spending in an uncertain economy. Rivals Palo Alto, ZScaler and CrowdStrike fell between 0.6% and 2.6%. Fortinet cut its annual revenue target on Thursday and said it expects current-quarter sales between $1.38 billion and $1.44 billion, below estimates of $1.50 billion, LSEG data showed.