Assalam o alaikum
What does CIH do?
Normally, CIH simply spreads itself. But on certain trigger dates, it detonates its warhead. The warhead wipes out your hard disk, and then tries to overwrite the computer's BIOS chip. Once the BIOS is overwritten, you will be unable to use your computer at all. Repair involves physically removing the BIOS chip and replacing it with a fresh one. On some computers, the BIOS chip is not removable, so it can only be replaced by swapping the entire motherboard.
Which operating systems are vulnerable?
CIH spreads under Windows 95 and Windows 98. DOS and Windows 3.x cannot spread CIH because they cannot run Windows 95/98 programs. Windows NT cannot spread CIH because the virus uses programming tricks that do not work under NT. The virus can infect Windows NT programs, but such programs will no longer run, and will therefore not be infectious themselves .
How can I prevent it?
Use reputable anti-virus software which can accurately identify CIH. Your goal is not just to avoid having your computer damaged by CIH on 26 April, but to avoid being infected at all - by CIH or any other virus.
Just change the date of your computer before 26 april.