Spanish police have caught their first mobile virus writer with the arrest of a 28 year-old man in Valencia.

The man allegedly wrote more than 20 different variants of the Cabir and Commwarrior worms, and sought to install them on mobile phones.

Police estimate that over 100,000 phones may have been infected with the malware, and said that the damage may cost mobile operators and phone owners millions of euros.

"Mobile phone viruses are not nearly as common as the malware that strikes Windows desktops on a regular basis, but they are just as illegal in their intent," said Graham Cluley, senior technology consultant at Sophos.

"Viruses are not harmless pranks; they cause real harm disrupting business and personal communications as well as destroying and stealing sensitive data.

"The computer crime authorities around the globe are becoming more experienced at tracking down hackers and virus writers and, given this latest arrest, malware authors should be asking themselves whether it is really worth taking the risk."

The viruses were installed by users who thought they were downloading erotic photos, sports information or antivirus software.

One of the clues that led Spanish police to the arrest was the frequent inclusion of personal names, including 'Leslie' which is thought to be the man's fiancée.