seeding PRNGs from the system clock is quite common. Using the system time as a source of entropy for generating secure random numbers is problematic because it

seeding PRNGs from the system clock is quite common. Using the system time as a source of entropy for generating secure random numbers is problematic because it's not random. You want sources that are "noisy" to contribute. Let's say we're generating some private key, and using the time as a source, and then writing the cert to a file, you'd probably be able to get a pretty good idea from the timestamp of that file what the system time was when the private key was generated.