Module directories with dot prefix

[artfulrobot]

I've noticed on some sites that my site/modules directory contains some duplicate module folders, same name but prefixed with a . 

The dot-prefix ones all seem to be very old, but I'm still not sure how they got there. Perhaps this is where the web UI installer places temporary copies and perhaps it wasn't able to complete and they got left over?

Can I safely remove the dotted ones?

Many thanks.

[Ivan Gretsky]

Those are backups created automatically by UI module installer/upgrader, you are right. You can safely remove them. Ignore them in .gitignore if you use git.