@ScubaAddict, the suspicion was on some competitor using MT to send such useless short visits. It lasted for 2 week then.
But I didn't see any pattern like traffic from one service provider as 100up says.It al looked very natural. But the number of direct visits on all those days were almost the same.
Now, I don't even think it is the sabotage work of any competitor.
GA does not report any traffic from spiders unless you adopt some special techniques. I do have a separate profile set up to monitor bots through GA (with the help of some code on the site) but you may not see them through a normal profile.