The Ministry of Defence has revealed that 658 laptops have been stolen over the past four years. It had previously claimed that 347 laptops were stolen between 2004 and 2007.
In addition a further 747 laptops have been lost in that period, the MoD said, rather than the 89 laptops previously claimed.
The department also disclosed 121 of its USB memory sticks, some containing sensitive information, have been lost or stolen since 2004.
The department uses six categories of classification for information - unclassified, restricted, confidential, secret, top secret and non-classified. Five of the missing USB sticks contained "secret" information. A further 81 contained restricted information.
The figures, broken down by year, show that 8 USB sticks were lost or stolen in 2007. But since January this year, 26 portable memory sticks had been either stolen or misplaced.
The figures emerged in response to Parliamentary questions from Liberal Democrat MP Sarah Teather and Conservative Shadow Defence Secretary Dr Liam Fox on loss of IT equipment in the MoD.
"This shows a shocking degree of incompetence across the entire Government," Teather commented. "It seems that this Government simply cannot be trusted with keeping sensitive information safe. It is frightening to think that secret MoD information can be lost or stolen."
Defence minister Bob Ainsworth said the department is investigating the details of all lost or stolen electronic media since 2003. The department has suffered a spate of data losses recently. In January, the department admitted 600,000 unencrypted records went missing when a laptop was stolen.
The revised laptop figures are the result of the Burton Review which "revealed anomalies in the reporting process".
Ainsworth said: "It should be noted that details of such incidents were not collated centrally before 2003 and therefore will not be available."