| UltimateCleaner | - | | - |
| UltimateDefender | - | | - |
| UltimateFixer | - | | - |
| UltimateSpyware | - | | - |
| Umisy.2322 | Category 1 | | 09-10-2001 |
| Unashamed | Category 1 | | 08-22-1995 |
| Unigray | - | | - |
| UNIX.comp | - | | 02-16-2002 |
| Unix.gwi | Category 1 | | 03-18-2002 |
| Unix.Penguin | Category 1 | | 03-04-2000 |
| Unsnared.814 | Category 1 | | - |
| UnSpyPC | - | | - |
| Upgrade Internet 2 Hoax | - | | 10-03-2000 |
| Urkel | Category 1 | | - |
| URLSpoof.Exploit | Category 1 | | 12-31-2003 |