Over 3 million new security threats were identified in 2009 or one every 10.8 seconds, according to research from a security firm.
The majority of spam and malware now comes from botnets, or automated software robots, says Network Box.
To keep your computer safe install one of our Best Buy security software suites
Another shift was an increase in targeted vulnerability attacks where hackers actively seek out security holes in applications, web browsers such as Internet Explorer 8 and Google Chrome and in company servers.
Microsoft not the only target for hackers
Historically, Microsoft has been the prime target for hackers but during 2009 their attention appears to have broadened. This has led to other big software companies reporting critical vulnerabilities in their programs.
Adobe, for example, announced vulnerabilities in its PDF and Acrobat programs. WordPress blogs have also been susceptible to multiple vulnerabilities leading to passwords being compromised.
Browsers such as Apple Safari, Mozilla Firefox and Opera have also announced critical vulnerabilities.
Worryingly, there’s also been an increase in the number of Trojans stealing personal data such as passwords, information from social networking sites and financial log in details.
Read our review of online banking security
Trojan threats on the rise
During 2010 computer users should watch out for banking Trojans such as Zeus and Urlzone, which re-writes your online bank statement to cover its tracks once the money has been taken and Clampi, which steals banking log-in details.
Sarah Kidner, editor of Which? Computing said: ‘Increasingly, you won’t see any physical signs that your computer is under attack. It’s imperative that everyone takes steps to secure their computer using our Best Buy security software and by installing updates for their operating systems and programs regularly.’
How to follow the latest Which? Tech news
Are you a Twitter user? Follow WhichTech on Twitter for regular tech tweets.
Prefer RSS? Don’t miss a thing with the Which? tech RSS feed.
For just the main headlines in newsletter form, sign-up to our weekly Which? tech email.
Apple iPad 2 3G data plans compared – find the best 3G plan for your iPad
Best Android tablets round-up – we look at the best iPad alternatives around
Best cheap laptops for under £500 – find the best laptop deals