Those who operate important online services should always consider more than one version of the domains that refer to the name of the service, product, or company name. This is especially true if the name contains letters that are similar to other letters, for example I and i, t and f, the symmetries b and d or p and q and so on.
A famous example in Iceland is when a pirated version of the Icelandic police's website was put on the Web under the fraudulent domain logregian.is (the real domain being logreglan.is).
A good example of a "positive blocking domain registration" is the domain arionbankl.is (notice the lowercase "L" at the end). It was registered by Arion Banki to increase the online security of its customers.
The lowercase "L" and uppercase "i" are visually similar and are therefore often used in deceptive domains, as the human eye can have a hard time noticing the difference between the letters. Please be aware of this and always read the domain name of any website you visit, and of any email address from emails you've received.