The Request-To-Send and Clear-To-Send (RTS/CTS) exchange has been used in Mobile Ad-hoc Networks (MANETs) to alleviate the hidden and exposed terminal problems. In such an exchange, the so-called Network Allocation Vector (NAV) indicates the current and future state of the channel. Unfortunately, this technique may suffer from virtual jamming by malicious nodes in the network. For example, malicious nodes may send periodic Spurious CTS (SCTS) packets with the sole purpose of forcing other nodes to update their NAV values and preventing them from using the channel. In this paper, we investigate the effect of such SCTS attacks and propose a solution, termed Carrier Sensing based Discarding (CSD). The CSD scheme serves as an add-on to the original RTS/CTS-based Medium Access Control schemes such as IEEE 802.11 DCF MAC. We further demonstrate the performance of our proposed scheme through analysis and the ns2 simulator.