Businesses are being warned that three <A HREF="http://news.zdnet.com/2100-1009_22-6153282.html?tag=nl.e589">Cisco Systems router operating-system vulnerabilities</A> have been discovered. The flaws found could enable a malicious individual to commit denial-of-service, or DoS, attacks against Web sites, according to a warning issued by the U.S. Computer Emergency Readiness Team. US-CERT's warning about the Cisco IOS issue says a remote attacker would be able to execute code on affected devices. Users are being told to upgrade to a fixed version of IOS, which stands for Internetwork Operating System.