How are virus infections like a "sneak attack"?

Viruses enter human body like an invader and uses the living cells to replicate causing infections in the cell or can damage it.

Explanation:

The attacks of viruses on the body of living organisms is compared with a 'sneak attack' as they invade the body and enters into a living cell to replicate themselves. This may cause damage or bring about changes in the cell causing sickness and infections.

They can hide themselves on our body attacking sneakily to harm the immune system to fight the infection. This stealth infection can result in fever, damaging immunity, disorder etc.