Dutch intelligence service AIVD has ruled 1,200 e-voting computers inadequate for next month's national elections after testing showed the machines could be be easily intercepted from 20 to 30 metres away.

Voters in large cities such as Amsterdam, Eindhoven, and Tilburg will now have to cast their ballot with pencil and paper, although some municipalities can still decide to use different polling computers.

The vulnerable machines are those made by manufacturer Sdu. The remaining 90 per cent of the nation's polling computers are made by Nedap. Although Dutch IT professionals in the Netherlands have demonstrated that these type of e-voting machines can also be secretly hacked using a simple radio receiver, the AIVD tested three of the four Nedap variants and determined that there is no real danger of "bugging".

Nedap says it is currently installing new microchips and software to prevent hackers manipulating the votes. Additionally, ballot computers for the November elections will be equipped with a "unique iron seal" to guarantee their reliability.

Research bureau TNO will perform random tests on the Nedap machines before they are used. ®