The number of personal computers that unknowingly host malicious "zombie" code has increased an astounding rate this year, according to a new report by antivirus software maker McAfee, reports CNET. Zombie, or "bot," incidents reached 13,000 from April through June, quadrupling the number in the previous quarter, according to McAfee, which estimates that 63 percent more machines were exploited by bot programs as well as spyware and adware in the first six months of this year than all of last year.

McAfee also reported a 12 percent increase in the number of new unwanted programs created in the past three months, compared with the previous three months. It also warned that researchers have discovered a new method for hacking cell phones using the Bluetooth wireless protocol.