How a working Graphics Card can get corroded ?

I have a MSI GTS 250 which am using continously from past 1 year. But last week i got no display on monitor problem. It has 2 more years of warranty remaining.
So submitted to MSI Service Center @ Secundrabad (DigiCare).
Today they replied card canot be repaired becoz the board has corrosion ??
How can a my card get corroded if am using it continously that too only in 1 year ???