The hacking was carried out to allegedly steal valuable data related to its customers and pricing.
Senior executives of Quadsys have pleaded guilty to their actions after a series of court hearings.
The court clerk was quoted saying: "All pleaded guilty to obtaining unauthorised access to computer materials to facilitate the commission of an offence.”
Facing hacking charges, Quadsys owner Paul Streeter, managing director Paul Cox, director Alistair Barnard, account manager Steve Davies and security consultant Jon Townsend appeared before Oxford Crown Court.
They admitted to “obtaining unauthorised access to computer materials to facilitate the commission of an offence."
The executives may face up to 12 months in prison or fines.
They were originally arrested in March last year on the grounds of their suspicious involvement in computer misuse, gaining unauthorised PC access, and "conspiracy to acquire and use criminal property."
Charges were also filed on them for conspiring to obtain the rival’s company pricing data.
In August, all the executives pleaded that they were not guilty to a one of the charges that accused them of "securing unauthorised access to computer material with intent.”
The charge is against the UK Computer Misuse Act 1990.
A new charge for securing access to computer material without criminal intent was added to the list following three plea and case hearings, The Channel reported.
Quadsys consultant Townsend pleaded guilty to the charge, which Cox did not plead guilty for charges of blackmail.
The court is scheduled to announce their sentencing on 9 September. Besides, it will also hear a second charge the deals with obtaining unauthorised access to computer materials with intent to commit an offence.
The clerk added: "That will be dealt with at sentencing; the prosecution will say what they would like to happen.”
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