weird, ls ?? need help!!!!!

Hi,

I compiled c program ( myp.c ---> myp ), when use 'ls' command, I can
see myp executable file. I shutdown my linux box, but after for some
hours, I log on my linux box again, go to the path where myp exists,
then use 'ls' command, I can not see it. use './myp' can not be run.
Then I compiled another file myp1.c ( myp1.c ---> myp1 ), I can see and
run ./myp1. then shutdown...

after for some hours, I log on my linux box again, go to the path where
myp and myp1 exist, use 'ls' command, I can see and use mpy again, but
can not see and find myp1, it's weird, can some one give me some advice
or hints or help?

Is my michine hacked?

Log files seem OK though (but not sure, maybe log files have been hacked
too).

I appreciate your kind help!!!

xbt