Barracuda Labs 2010 Midyear Security Report, presented at DEFCON 18 hacking conference in Las Vegas — studied the four search engines for about two months and reviewed more than 25,000 trending topics and almost 5.5 million search results — reports that "Overall, Google takes the crown for malware distribution – turning up more than twice the amount of malware as Bing, Twitter and Yahoo! combined when searches on popular trending topics were performed. Google presents at 69%; Yahoo! at 18%; Bing at 12%; and Twitter at 1%."
The study also cites an increase in rogue accounts on Twitter this year. The "Twitter Crime Rate" — the percentage of accounts created each month that Twitter later suspends — was 1.67% for the first half of 2010, with a high of 2.38% in June.