Cybercriminals choose the cheapest and easiest way to gain access to the corporate network. Fortunately, the path of least resistance also causes subtle changes in system resources and network behavior that an experienced network security professional can detect, said Barry Shteiman, director of security strategy at Imperva. Systems are constantly probed for configuration weaknesses and software vulnerabilities, but often all that is needed are stolen account credentials, obtained through a phishing attack against employees. Hackers are successful because systems are not being proactively monitored, Shteiman told CRN. These five signs should sound alarm bells that an intruder is already maintaining a presence on your systems.