Judges are currently considering an appeal brought by software giant Oracle against a decision made by a district court judge in California last year. In that case judge William Alsup ruled that Google could legitimately copy the function of computer code owned by Oracle because it did not copy the "specific code" that Oracle had used to achieve that functionality.

However, judges at the Court of Appeal may be set to overturn that decision, according to media reports.

"Federal Circuit sounds ready to reverse Alsup and find Java declaring code was copyrightable," Scott Graham, a reporter who attended the appeal hearing for US legal news publication The Recorder, tweeted. Graham said that one of the judges had asserted "repeatedly" that Alsup "was confused or misunderstood the law".

Reuters reporter Dan Levine, also present at the hearing, tweeted that the panel of judges "sounded skeptical of Alsup ruling against Oracle on copyrightability of Java APIs".

If the protection given to software source code by copyright laws is given greater scope, the US courts would have to determine whether Google's use of it was fair.

In the US the 'fair use' exemption in copyright law allows copyright material to be reproduced for the purposes of research and education, commentary, criticism and reporting.

Whether reproduction of copyrighted works is defensible in the US by the 'fair use' defence depends on the consideration of certain factors, including the purpose and character of use and whether it was for commercial gain or not, the nature of the copyrighted work itself, how much of the copyrighted work was reproduced and the effect of that use on the potential market for or value of the work.

Levine said that the Court of Appeals panel appeared likely to send any trial on the fair use issues back to district court for judge Alsup to rule on.

In 2010 Oracle initiated a case against Google claiming that the internet giant was guilty of infringing its copyrights and patents in how it used Java technology in its Android operating system. The company claimed that Google required a licence to use the Java platform but had not bought one, and that therefore "without consent, authorisation, approval, or license, Google knowingly, willingly, and unlawfully copied, prepared, published, and distributed Oracle America's copyrighted work, portions thereof, or derivative works".

Java is a technology that allows programmers to write computer code that will run in many computing environments. APIs enable applications, platforms and other system elements to communicate.

Oracle also claimed that Google was guilty of helping other companies that utilise the Android operating system - such as mobile phone device manufacturers - infringe its rights.

In a ruling last year Alsup said that Oracle could only claim copyright protection in the specific way it had implemented code, ruling that programming language specifications were not copyrightable. He ruled that because Google had implemented the code differently – albeit to achieve the same functionality – that use had not been copyright infringing in nature.

In papers submitted to the Court of Appeals, Oracle claimed that the Google had been able to "rush" its Android operating systems to market because it had copied "thousands of lines of original ... source code". The code belonged to Oracle's Java API technology which enables computer programs to function. Oracle also said Google had "paraphrased" the rest of its code and that its activity amounts to an infringement of its copyrights that has no 'fair use' defence.

Oracle has claimed that Alsup made a "basic legal error" in reaching his decision.

According to a Bloomberg report, Google's legal representative told the Court of Appeals that the company wrote 15 million original lines of source code for the Android operating system. The company legitimately used "structural" elements of Oracle's code only before writing its own code to provide functionality, the company has argued.

The High Court in England and Wales recently confirmed a previous ruling by the Court of Justice of the EU that the way computer programs operate is not copyrightable. This is because computer program functionality is not "a form of expression" and therefore does not qualify for protection, it ruled.