time bomb

Short definition from Wiktionary

Noun

1. 1
   A bomb that has a mechanism such that detonation can be preset to a particular time.
2. 2
   A malicious program designed to perform a destructive action at a certain date or time.
3. 3
   A situation that threatens to have disastrous consequences at some future time.
4. 4
   Alternative form of time bomb.