Pathology, eye and audiology services have been affected by the bug which originated in an email attachment.
Mary Sherry, chief operating officer for Royal Berkshire NHS Foundation Trust, said a number of outpatient appointments also had to be rescheduled.
The trust said the virus has not affected patients' data.
According to the trust, priority has been given to patients who have the most urgent need or who are ready for discharge pending pathology results.
Ms Sherry added: "At the same time, the trust's services remain under pressure because of the volume of patients needing emergency care and the demand for our services and for beds remains high.
"The trust has locked down its network to protect it from any further intervention and informed the relevant authorities.
"Teams are working around the clock to resolve this issue and continue to protect the trust's network."
The virus is believed to be a variant of a known XP bug designed to disrupt services.

The 68-year-old was discovered in Fairisle Place in the Moray town at about 00:30 on Sunday.
He was taken to Dr Gray's Hospital in Elgin but died later that day.
Police said inquiries were ongoing to establish how he sustained his injuries and the death was being treated as "unexplained".
Det Ch Insp Kevin Walker, who is leading the inquiry, said: "Our thoughts are obviously with this man's family at this sad time.
"Our inquiries are continuing to establish the exact circumstances leading up to his death and at this stage his injuries are still being treated as unexplained.
"Several members of the public have already assisted with our investigation and I would like to thank them for their help.
"I would still encourage anyone who saw a man fitting his description, however, to please contact police if you think you have information which could help."
The man, who had white hair with a greying beard, was wearing a checked shirt, blue jeans and a dark-coloured hooded top.

In a festive season where most of our big retailers did better than expected, M&S stood out, finally shrugging off its clothing sales hoodoo.
Clothing sales have been in decline - and often sharp decline - for the past five years, with the exception of one positive quarter two years ago.
Over Christmas, however, like-for-like sales were up 2.3%, although the company was quick to point out that 1.5% of that was down to how Christmas fell, which meant there were five extra trading days compared to the relevant period a year earlier.
Even so, a 0.8% increase is not to be sneezed at, and is evidence perhaps that the back-to-basics reforms of chief executive Steve Rowe, which include hundreds of job losses at head office and the closure of most of the international stores, is having some effect.
M&S beats Christmas sales forecast
Tesco hails 'strong progress'
One good quarter doesn't make a revival, but a halt to the seemingly inexorable decline will give shareholders encouragement.
Retail analysts say Mr Rowe's formula - a concentration on the basics - is a welcome contrast to the recent past, where management introduced eye-catching fashion and made mis-steps online.
The real test will be at the next quarterly update, where the calendar is against Mr Rowe - just as he benefited at Christmas, he misses out next time.
If he can turn in another positive number on clothing, there will be substance to the M&S revival.
Elsewhere, there was good news tempered with caution about the coming year.
This was best expressed at the John Lewis Partnership, which reported like for like sales growth of just under 3% at both the department store chain and the grocery business, Waitrose.
Profits for the full year are likely to be up, but Sir Charlie Mayfield, the partnership's chairman, took the unusual step of warning staff their bonuses would be smaller than last year.
The culprits? The pressure caused by a weaker pound and the need to invest heavily in new products.
A number of operations have been postponed at Royal Berkshire Hospital due to a computer virus.
[NEXT_CONCEPT]
An elderly man found with serious head injuries in a street in Lossiemouth has died in hospital.
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Marks and Spencer has turned out to be this year's surprise Christmas package.