Ministry of Defence staff lost or had stolen 340 laptops worth more than £600,000 in the last two years, figures have revealed.
A total of 593 CDs, DVDs and floppy disks, 215 USB memory sticks, 96 removable hard disk drives and 13 mobile phones have also gone missing from the department since the release of a scathing report into MoD data losses.
Only one in five of the hi-tech devices that disappeared was encrypted, leading security experts to criticise the "cavalier attitude" to the protection of data.
The MoD had the worst record of 11 government departments surveyed in Freedom of Information requests made by technology consultants Lewis Communications.
In total the ministries reported the loss of 518 laptops, 131 BlackBerrys or iPhones, 104 mobile devices and 932 electronic storage devices over the past two years, at an estimated cost to the taxpayer of £781,453.
The MoD was strongly criticised in a report by Sir Edmund Burton, published in June 2008, for security lapses that led to the theft of a Royal Navy laptop containing records of 600,000 recruits and potential recruits to the armed forces.
Between June 2008 and the end of May this year, 220 of the department's laptops were lost and 120 were stolen. They were worth an estimated £612,000. Of these 157 - less than half - were encrypted, although 25 of the computers were later found.
The MoD put the total value of the electronic devices that disappeared during this period at £620,193, of which £45,804 of equipment was recovered. Nine members of staff were disciplined as a result of the losses, the department revealed.
The figures suggest the MoD's record has not improved significantly since July 2008, when it admitted that 658 laptops had been stolen and 89 lost in the previous four years.
Other ministries include the Department for Transport, which said it lost or had stolen 38 laptops, 39 PDAs including BlackBerrys, 21 mobile phones and two USB memory sticks, at a cost of £49,318. Two members of staff were disciplined.