| # | Family Of Threats | Threat Category |
| 1 | Win32/Rotbrow | Trojan Downloaders & Droppers |
| 2 | Win32/Alureon | Misc. Trojans |
| 3 | Win32/Sefnit | Misc. Trojans |
| 4 | Win32/Tracur | Misc. Trojans |
| 5 | Win32/Sirefef | Misc. Trojans |
| 6 | Win32/Zbot | Password Stealers & Monitoring Tools |
| 7 | JS/Medfos | Misc. Trojans |
| 8 | Win32/Winwebsec | Misc. Trojans |
| 9 | Win32/Vobfus | Worms |
| 10 | Win32/Conficker | Worms |
- The most common threat family infecting computers in the United States recently was Win32/Rotbrow, which is a trojan that installs browser add-ons that claim to offer protection from other add-ons. Rotbrow can change the browser’s home page, and can install the trojan Win32/Sefnit. It is commonly installed by Win32/Brantall.
- The second most common threat family infecting computers in the United States recently was Win32/Alureon, which is a data-stealing trojan that gathers confidential information such as user names, passwords, and credit card data from incoming and outgoing Internet traffic. It may also download malicious data and modify DNS settings.
- The third most common threat family infecting computers in the United States recently was Win32/Sefnit, which is a family of trojans that can allow backdoor access, download files, and use the computer and Internet connection for click fraud. Some variants can monitor web browsers and hijack search results.
- The fourth most common threat family infecting computers in the United States recently was Win32/Tracur, which is a trojan that downloads and executes arbitrary files, redirects web search queries to a malicious URL, and may also install other malware.
Source: Microsoft Security Intelligence Report
