Most boot sector viruses detected by some of the best commercial antivirus software such as Symantec's Norton Antivirus, Microsoft's Security Essentials, or Kapersky's Antivirus can not be removed by these applications. And in many cases a boot sector virus is capable of alluding these applications unless the drive is connected to a clean system that has the AV software actively running.
What is a boot sector virus? This is a computer virus that infects a diskette or hard drive in the area which contains information about the configuration of the disk. The boot sector is used by many computer operating systems to determine how to access the diskette or drive. These viruses replace the critical boot sector program used to start the computer with their own malicious program often causing frequent computer crashes, allowing other malware infections, and performance issues.