Why is the virus called the boot? Because he's at startup immediately loaded into memory and intercepts all system control. I'm sure many have faced such a problem that after visiting some, even innocuous sites, computer during the next boot has issued a warning that it is locked, ostensibly for visiting porno sites, or spam, or other negative actions.
Of course, this is nothing when unlocked will not , as such viruses laid even this possibility. Anti often powerless against them, as they are run immediately when the system boots, blocking all anti-virus and security software. So how do you deal with them?