Why is the reinstalled system still virus

Why is the reinstalled system still virus?
Answer:
Although the system is reinstalled, if the C drive is not formatted, or other Partitions (such as D, E, etc.) still have viruses. If you do not install anti-virus software to scan the entire hard disk, you must not read the D, E disk and other partitions, otherwise it may be poisoned again.
Some viruses will infect the hard drive master bootloader, causing your hard drive to re-infect after booting.
Also, in the case of security software such as "security guards" such as "360 Security Guardian", "Jinshan Guardian", if you have already been online or installed, you may be bundled with malware. Software, then it will re-infect the virus, causing the browser to work abnormally.
It is recommended to format the C drive to reinstall the system, then use the fdisk /mbr command to clean up the main boot area of ​​the hard drive, then install the anti-virus software in the C drive and upgrade to the latest virus database, and then scan the entire hard drive. After cleaning up the virus, install ““360 Security Guardian”, “Jinshan Guardian” or malware cleaning assistant, and block the malware, you can operate the computer as usual.