Short URLs often circumvent the intended use of
top-level domains for indicating the country of origin; domain registration in many countries requires proof of physical presence within that country, although a redirected URL has no such guarantee.
Abuse URL shortening may be utilized by
spammers or for illicit internet activities. As a result, many have been removed from online registries or shut down by web hosts or internet service providers. According to Tonic Corporation, the registry for .to domains, it is "very serious about keeping domains spam free" and may remove URL shortening services from their registry if the service is abused. In addition, "u.nu" made the following announcement upon closing operations: The last straw came on September 3, 2010, when the server was disconnected without notice by our hosting provider in response to reports of a number of links to child pornography sites. The disconnection of the server caused us serious problems, and to be honest, the level and nature of the abuse has become quite demoralizing. Given the choice between spending time and money to find a different home, or just giving up, the latter won out. Google's url-shortener discussion group has frequently included messages from frustrated users reporting that specific shortened URLs have been disabled after they were reported as spam. A study in May 2012 showed that 61% of URL shorteners had shut down (614 of 1002). The most common cause cited was abuse by spammers.
Linkrot The convenience offered by URL shortening also introduces potential problems, which have led to criticism of the use of these services. Short URLs, for example, will be subject to
linkrot if the shortening service stops working; all URLs related to the service will become broken. It is a legitimate concern that many existing URL shortening services may not have a sustainable business model in the long term. together with twenty collaborating companies (initially), whose short URLs will be preserved by the project.
Blocking and banning Some websites prevent short, redirected URLs from being posted. In April 2009, TinyURL was reported to be blocked in
Saudi Arabia.
Yahoo! Answers blocks postings that contain TinyURLs, and
Wikipedia does not accept links by any URL shortening services in its articles. The
Reddit community strongly discouragesand in some subreddits, outright bansURL shortening services for link submissions, because they disguise the origin domain name and whether the link has previously been submitted to Reddit, and there are few or no legitimate reasons to use link shorteners for Reddit link submissions.
Privacy and security A short URL obscures the target address and can be used to redirect to an unexpected site. Examples of this are "
rickrolling", and redirecting to
shock sites, or to affiliate websites. The short URL can allow blocked URLs to be accessed, bypassing site
blocklists; this facilitates redirection of a user to blocked scam pages or pages containing malware or XSS attacks. TinyURL tries to disable spam-related links from redirecting.
ZoneAlarm, however, has warned its users: "TinyURL may be unsafe. This website has been known to distribute spyware." TinyURL countered this problem by offering an option to view a link's destination before using a shortened URL. This ability is installed on the browser via the TinyURL website and requires the use of cookies. A destination preview may also be obtained by prefixing the word "preview" to the URL of the TinyURL; for example, the destination of is revealed by entering . Other URL shortening services provide a similar destination display. Security professionals suggest that users check a short URL's destination before accessing it, following an instance where the shortening service cli.gs was compromised, exposing millions of users to security uncertainties. There are several web applications that can display the destination URL of a shortened URL. Some URL shortening services filter their links through bad-site screening services such as
Google Safe Browsing. Many sites that accept user-submitted content block links, however, to certain domains in order to cut down on spam, and for this reason, known URL redirection services are often themselves added to spam blocklists. Another privacy problem is that many services' shortened URL format is small enough that it is vulnerable to brute-force search. Many people use URL shorteners when they share links to private content, and in fact many web services like Google Maps have offered automatic generation of shortened links for driving directions that reveal personal information like home addresses and sensitive destinations like "clinics for specific diseases (including cancer and mental diseases), addiction treatment centers, abortion providers, correctional and juvenile detention facilities, payday and car-title lenders, gentlemen's clubs, etc."
Additional layer of complexity Short URLs, although making it easier to access what might otherwise be a very long URL or user-space on an ISP server, add an additional layer of complexity to the process of retrieving web pages. Every access requires more requests (at least one more DNS lookup, though it may be cached, and one more HTTP/HTTPS request), thereby increasing latency, the time taken to access the page, and also the risk of failure, since the shortening service may become unavailable. Another operational limitation of URL shortening services is that browsers do not resend POST bodies when a redirect is encountered. This can be overcome by making the service a
reverse proxy, or by elaborate schemes involving cookies and buffered POST bodies, but such techniques present security and scaling challenges, and are therefore not used on
extranets or Internet-scale services. ==Notable services==