Me and my friends came up with an idea, and we're going through with it. Does a US patent similiar to our idea affect us if we're filing it in a different country?
YES it will affect your application. In what extent is matter of analysis and claims you are filing.
NO Patent :- If the subject matter was published in any publicly accessible document anywhere in the world (journal; patent; patent application; news etc.) prior to the patent applicant filing.
NO Patent :- If subject matter was publicly known in united states, but not necessarily patented or published, prior to the patent applicant filing.
Note:-There are certain rules which allow a person to file and get patent if disclosure is by inventor itself under certain special circumstances and time limits. but it certainly effect the international filings and grant.
Yes, it will most likely affect you. Most other countries worth the trouble and cost of obtaining a patent in have laws in place that ban patents that are either directly disclosed or made obvious by prior art in any place. Remember, the PCT (patent cooperation treaty) is joined by many larger nations, and they are bringing their laws more into accord with it over time. The AIA (first-to-file, etc.) in the US was primarily a result of various patent treaties we've signed.
If a US patent exists that either directly discloses your idea or makes it obvious to a person skilled in the art (i.e. someone who is reasonably competent in the industry/field of your idea) then it will most likely ban your idea from being patented in most other countries. There are some countries that tend to ignore prior art, just as there are some countries that grant you a patent without really examining your application, and thoroughly examine your application only if your patent is actually challenged.
This doesn't necessarily mean that you can't market your idea. A patent only bans marketing in the country patented in and if it is actually claimed in the patent.