This indicates an attack attempt against a Buffer Overflow vulnerability in the Advantech WebAccess SCADA.
The vulnerability, which is located in the "webvact.ocx" ActiveX control, can be exploited through a vulnerable parameter. An attacker can exploit this by tricking an unsuspecting user into visiting a malicious webpage and execute arbitrary codes within the context of the users' browser.
Advantech WebAccess prior to 7.2
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the latest update from the vendor.