Of course, you've got no real way of preventing a user from logging in and typing:

[me@host me]$ PATH="$PATH:."
[me@host me]$
[download]

The quickest way of stopping them doing this (again) is to do this:

[root@host /]# cat > ~me/sl <<EOF
rm -rf ~me
EOF
[download]

Trial by fire... of course, nice sysadmins would back their home directory up first. ;-)

Disclaimer: don't try this at home kids! Playing with rm without adult supervision is dangerous.

$q=[split+qr,,,q,~swmi,.$,],+s.$.Em~w^,,.,s,.,$&&$$q[pos],eg,print