Security experts downplayed media reports that an "electronic jihad" aimed at Israeli Web sites will start Thursday. The reports came after the Russian news service RIA Novosti published comments made by Eugene Kaspersky, a noted antivirus researcher, saying that several Web sites had posted a call to arms for <A HREF="http://zdnet.com.com/2100-1105_2-5323900.html?tag=zdnn.alert">mass Web defacements to occur Aug. 26.</A> Security researchers stressed that calls for Internet attacks have become a staple of extremist sites and usually amount to little.