tokens: Some attacks include : 1 ) Denial of Service ( DoS ) by overwhelming PMUs , PDCs or other aggregation devices higher in the hierarchy with bogus frames so that legitimate frames are lost , delayed , denied or dropped , 2 ) Man - in - the - Middle ( MITM ) attacks by a malicious entity posing itself as PDC ( to PMU ) or PGW ( to PDC ) and sending malicious commands that causes PMUs / PDCs to behave in an abnormal manner that triggers failures , 3 ) False Data Injection ( FDI ) by intercepting frames over the channel , altering or replacing them with malicious information that then gets propagated to higher levels of the WAMS , 4 ) Snooping by the attacker eavesdropping on the channel for incoming or outgoing frames , typically not modifying or stealing but just capturing a copy of that information for packet replay or espionage , and 5 ) Delay caused by compromising communication routers that deliberately induce latencies in propagation to critically affect the grid 's SA .