A hacker group has brazenly ramped up its antics as unrelenting waves of cyberattacks expose how poorly defended many networks are against internet marauders.

Three Web sites belonging to the US Department of the Treasury have been hacked to attack visitors with malicious software, security vendor AVG says.

Iran's Islamic Revolutionary Guards Corps hacked into 29 Web sites affiliated with U.S. espionage networks, Iran's semi-official Fars News Agency reported on Sunday.

At the RSA Conference in San Francisco last week, security vendors pitched their next-generation of security products, promising to protect customers from security threats in the cloud and on mobile devices. But what went largely unsaid was that the industry has failed to protect paying customers from some of today's most pernicious threats.

The Chinese government is likely behind recent cyberattacks on U.S. government Web sites and on U.S. companies in an apparent effort to quash criticism of the government there, an expert on U.S. and Chinese relations said Wednesday.

Imagine a scenario in which a downloadable application turns smartphones into network-clogging bots, causing U.S. mobile-phone networks to fail, and eventually spreads to the wired Internet.

China on Tuesday denied any role in alleged cyberattacks on Indian government offices, calling China itself the biggest victim of hackers.

Juniper Networks and Symantec said Thursday that they were investigating a widespread cyber-espionage incident that has hit dozens of technology companies, including Google and Adobe.

More than anyone else, Jaak Aaviksoo has first-hand knowledge of what a cyberwar might feel like. In April 2007, Estonia's banking, media and government presence online was disrupted by several waves of distributed denial of service attacks that knocked services offline. The country is heavily wired -- 90 percent of all financial transactions are conducted over the Internet and 70 percent of the population files their tax returns electronically -- so the incident was widely felt by the country's 1.3 million citizens.