Running pirated software can leave companies open to hackers, a security firm claimed today.

The warning follows research by the Business Software Alliance claiming that a third of corporate PCs are running pirated software.

According to the research, 35 per cent of computers run at least one illegal program. Computer users in China and Russia are the worst offenders with over 80 per cent of computers running pirated software.

Security firm Sophos noted that pirated software can leave business networks open to attack as cyber-criminals are provided with an additional route to infection.

"Putting aside the obvious legal issues, piracy can have a real impact on a company in terms of security," said Graham Cluley, senior technology consultant at Sophos.

"It is not enough to make sure that all PCs are running legitimate copies of Word; businesses must also control what programs their employees are downloading, installing and running."

Patching against software vulnerabilities is key to any good IT security policy, according to Cluley, but becomes near impossible with pirated software.

"Pirated software downloaded from dodgy websites or bought from a man in an alley will not come with technical support, and may even be virus infected," he said. 

Cluley added that running pirated software on corporate networks can also have severe repercussions on the network infrastructure, hogging valuable bandwidth and network resources.

"Businesses simply cannot afford to ignore piracy," he said. "The corporate network is the backbone of any company and if you allow users to run anything they like on it, whether illegal or not, you should not be surprised when it breaks."