Piper Jaffray analyst Andrew Nowinski says the security stocks he covers have underperformed the Nasdaq composite despite delivering "solid beat-and-raise" results. With the exception of Fortinet (FTNT) and Imperva (IMPV), the remaining security stocks within Nowinski's security coverage universe have all underperformed the Nasdaq. Symantec (SYMC) has underperformed by 0.7%, CyberArk by 1.6%, Proofpoint (PFPT) by 5.3%, Palo Alto by 7.4%, FireEye (FEYE) by 8.4% and Barracuda by 36.7%, Nowinski tells investors this morning in a research note. Investors remain concerned with the potential for a moderation in spending, the analyst believes. However, his channel checks with resellers suggest demand should remain strong for the next 12 months. Nowinski views the recent pullback in the sector as an attractive buying opportunity. Stocks with the most attractive valuations include Barracuda Networks (CUDA), CyberArk Software (CYBR), Fortinet (FTNT) and Palo Alto Networks (PANW), Nowinski writes. Wells Fargo this morning upgraded shares of CyberArk to Outperform.