Saudi Arabia recently arrested another ten people (eight Saudis, a Lebanese, and a Turk) and charged them with spying for Iran. The latest arrests were the result of information obtained from some of the 17 similar arrests made two months ago (16 Saudis and one Iranian). Iran denied that any of the 27 arrested for spying in Saudi Arabia last month worked for them. That may be true but so many Iranian agents have been caught by Arab police in the last few years that it is generally accepted that the Iranian espionage efforts continue in Arab countries. Arabs see Iranian efforts to develop nuclear weapons as aimed primarily at them. Iran has dominated the region for thousands of years and many Iranians believe that a new Iranian empire would be possible if Iran controlled all the oil in the region and had nukes to help make that happen.
Iran accuses the Saudis of inventing these espionage plots as a way to create more anti-Shia sentiment inside Saudi Arabia. That is certainly happening, whether intended or not. Nevertheless the Saudis seem to have a lot of evidence on the latest batch of 27 suspects. The Saudis have traced payments from Iran to the 27. Apparently the 27 were low level operatives, being paid to report on the status of various strategic military and economic facilities. This is the sort of thing that can be collected by anyone passing by. Cell phones make it easy to casually take pictures as well and transmit them to their handler. Several of those arrested are known to have made regular visits to Iran, where they could have delivered data via tiny (and easy to hide) MicroSD cards (used in phones, cameras, and the like).
The Saudis won’t reveal exactly how they caught the 27, something the Iranians would like to know. The Saudis may have had assistance from Western and even Israeli intelligence. A likely method was simply monitoring the Internet and telephone networks, or one of the 27 may have gotten sloppy and attracted the interest of Saudi counter-intelligence or security personnel. The 27 will be questioned and investigated for months before they are prosecuted.