'Passing off' has a specific legal meaning and I think that more information would be needed to see if what they're doing can be defined as that.
Usually they would have to be offering different goods under the same name as a competitor - and thereby misleading the customer.
For example fake Nike t-shirts. Passing off not only infringes trademark (whether registered or unregistered trademark), but it can also mislead about the quality of the service or goods that the public think they are buying.
I really don't know how similar the services that you and the other company are providing, but the names aren't identical by a stretch.
For example, we know there's Burger King and places called Kingston Burger (a place in London). Same generic elements in the name. Even though they sell the same products and have similar names this isn't passing off (or even trademark infringement in my opinion)
cantufind.com v ufindus.com - they are pretty different aren't they?
if they were called "canufind.com" then I would think that would give more of a case to them infringing your trademark and possibly passing off... In fact I just checked and canufind.com exists
... Page rank of 5 as well ???
As for you and 'ufindus.com' you both share "ufind" so if you can show a right for the trademark "ufind" (whether you have paid to formally register it, otherwise if you have established yourself with that name in the marketplace before anyone else) then you might have a claim for them infringing on your trademark - but not passing off - again this is only my opinion. And it really depends on if they are causing confusion with your current or potential customers.
But ufind is also pretty common out there:
ufind - Accurate Search Results
UseekUfind
U.find / Localização e Serviços por celular
CanUFind.Com
...plus a bunch more
Passing off is a very narrow crime, and you would have to prove that they are somehow misleading your customers into thinking they are you. Usually by infringing on your trademark type or image and providing the same services or products.
Hope this helps a little. Goodluck
