[Ynet] Iranian hackers have become increasingly aggressive and sophisticated, moving from disrupting and defacing US websites to engaging in cyber espionage, security experts say.According to Silicon Valley-based cybersecurity company FireEye Inc, a group called the Ajax Security Team has become the first Iranian hacking group known to use custom-built malicious software to launch espionage campaigns. Ajax is behind an ongoing series of attacks on US defense companies and has also targeted Iranians who are trying to circumvent Tehran's Internet censorship efforts, FireEye said on Tuesday.