The CPI-M on Sunday offered security for the four whistle-blowers in Madhya Pradesh's Vyapam scam, being now probed by the Central Bureau of Investigation following the Supreme Court's directive.In a statement here, the Communist Party of India-Marxist's (CPI-M) state secretary Badal Saroj said Ashish Chaturvedi, a whistle-blower from Gwalior, was threatened by Bharatiya Janata Party leader Hari Singh Yadav. A police complaint has also been filed about the threat.Pointing to the threat to Chaturvedi's life, Saroj said his party wanted to provide security to Chaturvedi. He said the same offer stands for three other whistle-blowers -- Anand Roy, Paras Sakhlecha and Prabhat Pandey.