A double layered security net has been thrown around Delhi's more than 20,000 electronic voting machines (EVMs), officials said Friday.At least two companies of the Central Industrial Security Force (CISF), comprising around 200 personnel, along with some other paramilitary forces are assisting Delhi Police personnel to guard a total of 21,967 EVMs kept in seven counting centres, one in each parliamentary constituency.Sources said the voting machines, which will be kept sealed till the day of counting votes May 16, will be guarded round the clock by at least 50 security men."There is a two-layer security arrangement at every counting centre where the EVMs are kept. The inner security is being provided by paramilitary forces while the outer security is under the Delhi Police," said the official.A total of 150 candidates, including 57 Independents, were in the fray for the seven Lok Sabha seats from Delhi.