互聯(lián)網(wǎng)解決方案提供商思科在其《年度安全報告》中稱，由于黑客不斷想出控制用戶計算機(jī)的新途徑，被控制的計算機(jī)每天會發(fā)送大量垃圾郵件，這些垃圾郵件數(shù)量達(dá)到近2000萬封，占全部電子郵件總量的約90%。該報告指出，美國是最大的垃圾郵件“源頭”，占到了垃圾郵件總量的17.2%；土耳其和俄羅斯分列第二、三位，所占比例分別為9.2%和8%。

    Armies of hijacked computers are flooding the world with spam as hackers devise slicker ways to take over unwitting people's machines, according to a report released on Monday.

    Virus-infected computers are woven into "botnets" used to attack more machines and to send sales pitches to e-mail addresses in low-cost quests to bilk readers out of cash.

    "Every year we see threats evolve as criminals discover new ways to exploit people, networks and the Internet," said Cisco chief security researcher Patrick Peterson, who was involved in drafting the report.

    Junk e-mail, or spam, accounts for nearly 200 billion messages daily, approximately 90 percent of email worldwide, according to the Cisco Annual Security Report.

    The US is the biggest source of spam, accounting for 17.2 percent messages. Turkey and Russia ranked second and third, accounting for 9.2 percent and 8 percent spam respectively, according to Cisco.

    This year, botnets were used to inject an array of legitimate websites with an IFrames malicious code that reroutes visitors to websites that download computer viruses into their machines.

    "The botnet is, in many cases, ground-zero for online criminal threats," Peterson said. "Using malware to infect someone's computers is an incredibly common mechanism and harnessing them all together is a way they do their click fraud, spam emails, and data stealing."

    Online criminals are turning botnets on web-based e-mail accounts. Hackers are "reputation hijacking" by using botnets to figure out weak passwords protecting web-based e-mail accounts, according to Peterson.

    Weak passwords consist of family names, birthdays, home addresses or other terms considered relatively easy to deduce.

    Once access is gained to legitimate e-mail accounts, a plethora of spam messages are sent in the owners' names.