If you don't want to be hacked:

1) Update to MemHT 4.0.1 if you have an old version
2) Apply the available pathches:
- http://www.memht.com/news_118_Small-fix-4-0-1.html
- http://www.memht.com/news_120_Another-small-4-0-1-fix.html
- http://www.memht.com/news_136_Small-fix-for-MemHT-Portal-4-0-1.html
3) Disable the ImageUp addon
4) Check for unknown files in your ftp: uploads, avatars, gallery, imageup folders

If you do this, you should be safe, else... take your risks (and don't complain here)