Malicious URL Blocking
The big difference between F-Secure's suite and the standalone antivirus is the addition of browser protection. This component blocks access to malware-hosting URLs, and it did well in testing.
I started with a collection of newly-discovered malicious URLs supplied by MRG-Effitas, none of them more than four hours old. Some had already vanished, but I kept launching them one after another until I had results for 100 still-working URLs.
F-Secure blocked an impressive 73 percent of the malicious URLs. Only Trend Micro Internet Security 2015 at Trend Micro and avast! Internet Security 2014 at Avast have done better, with 80 percent and 79 percent, respectively.
F-Secure's standalone antivirus lacks browser protection, but it did manage to wipe out 34 percent of the malicious payloads during or immediately after download. That's just slightly better than the average blocking rate among current programs.
So-So Phishing Detection
The browser protection component also serves to steer users away from visiting phishing sites—fraudulent sites that attempt to steal login credentials. However, it wasn't nearly as effective as it was against malware-hosting URLs.
I started by collecting suspected phishing URLs from various sites. Then I launched each simultaneously on five test systems. Naturally one test system relied on F-Secure's protection. Another used Norton Internet Security (2014) at Amazon. The remaining three relied on the built-in protection offered by Internet Explorer, Firefox, and Chrome. I repeated the process several times until I had data on more than 100 verified phishing URLs.
The URLs are different every time, so rather than report percentages directly, I report the difference between the tested program and the rest. F-Secure didn't do so well. Its detection rate came in 39 percentage points behind Norton, 24 points behind Chrome, and 7 behind Firefox. It did beat Internet Explorer by 9 percentage points, but that's small consolation. If you use F-Secure, don't turn off phishing protection in your browser.
Miniscule Performance Hit
Some of us remember the days when installing a security suite meant saying goodbye to speedy system performance. Modern suites tend to have a much lighter touch. However, some, like F-Secure, are truly lightweight when it comes to their effect on system performance.
Averaging 100 tests with no suite and 100 with F-Secure loaded, I found that boot time increased by just 8 percent. That's the time from the start of the boot process until the system is ready to use, defined as 10 seconds in a row with CPU usage below 5 percent. The average suite slows boot time by 20 percent.
I averaged multiple runs of a script that moves and copies files (big ones!) between disks, with and without F-Secure. I couldn't measure any slowdown. Another script that zips and unzips the same file collection repeatedly took just 3 percent longer. Webroot SecureAnywhere Internet Security Plus (2014) is one of the very few suites with even less impact than F-Secure.
A Lightweight Suite
F-Secure Internet Security 2015 is a lightweight suite in more ways than one. Yes, it had a minuscule effect on system performance. But it also lacks a full-scale firewall, and the Facebook protection it used to have is now gone.
It's a decent product, with good malware blocking and excellent detection of malware-hosting URLs. However, I'd still recommend Editor's Choice Norton Internet Security (2014). If you're after a mega-suite with all the trimmings, consider Bitdefender Total Security 2015 or Webroot SecureAnywhere Internet Security Complete (2014), two other Editors' Choice options.
Note: These sub-ratings contribute to a product's overall star rating, as do other factors, including ease of use in real-world testing, bonus features, and overall integration of features.