A method for detecting viruses on a handheld computer comprising: scanning data from a handheld computer for viruses with a virus detection program; characterised by the following steps taking place before scanning: linking said handheld computer into communication with a computer system having a virus detection program for running thereon; reading data from the handheld computer; storing said data at least temporarily on the computer system; and characterised in that said scanning of said data for viruses with the virus detection program takes place on said computer system; and further characterised by updating data held on the handheld computer, after said scanning, wherein said updating is based on the results of the scanning by writing cleaned data to the handheld computer and deleting infected data; synchronizing said data between the handheld computer and the computer system; and determining a priority setting of the synchronizing and the scanning, and performing the synchronizing or the scanning based on the priority by performing the synchronizing before the scanning if the synchronizing has a higher priority and performing the scanning before the synchronizing if the scanning has a higher priority. scanning data from a handheld computer for viruses with a virus detection program; characterised by the following steps taking place before scanning: linking said handheld computer into communication with a computer system having a virus detection program for running thereon; reading data from the handheld computer; storing said data at least temporarily on the computer system; and characterised in that said scanning of said data for viruses with the virus detection program takes place on said computer system; and further characterised by updating data held on the handheld computer, after said scanning, wherein said updating is based on the results of the scanning by writing cleaned data to the handheld computer and deleting infected data; synchronizing said data between the handheld computer and the computer system; and determining a priority setting of the synchronizing and the scanning, and performing the synchronizing or the scanning based on the priority by performing the synchronizing before the scanning if the synchronizing has a higher priority and performing the scanning before the synchronizing if the scanning has a higher priority. linking said handheld computer into communication with a computer system having a virus detection program for running thereon; reading data from the handheld computer; storing said data at least temporarily on the computer system; and characterised in that said scanning of said data for viruses with the virus detection program takes place on said computer system; and further characterised by updating data held on the handheld computer, after said scanning, wherein said updating is based on the results of the scanning by writing cleaned data to the handheld computer and deleting infected data; synchronizing said data between the handheld computer and the computer system; and determining a priority setting of the synchronizing and the scanning, and performing the synchronizing or the scanning based on the priority by performing the synchronizing before the scanning if the synchronizing has a higher priority and performing the scanning before the synchronizing if the scanning has a higher priority.