Browsing the Internet at work is not inherently a bad thing
Many people learn about emerging technologies through social media like twitter , they learn how to solve problems through Q/A sites like: How should I deal with a subordinate who is distracted and not performing well?, even reading web comics like xkcd.com can be quite educational and a much needed emotional reset similar to taking a smoke break, but potentially more productive.
In most cases when an IT worker is "wasting time on the web" at work it is not that they are reading articles that is the problem but how much.
In many cases, it also turns out that the perceived problem is that people are animals of habit. You may always have enough downtime at a certain time of day to check on him which just so happens to be when he also has a bit of down time to read articles; so, just because you routinely "catch him in the act" does not mean that that is what he is normally doing. If instead you should be looking at his projects: how much he is backlogged, how many hours a day he is devoting to tasks, and are those tasks are taking as long as they should.
Don't address the Problem, address the Solution
The best way to do this is making your IT department use some manner of CRM for tracking the work they do. Normally CRMs are used for tracking the work consulting firms do for outside companies, but even if this is an internal IT department, a CRM will help them organize information about your infrastructure, track projects statuses, and most importantly as far as your question is concerned: log how much work he is actually getting done.
Then if the data shows he is in fact slacking, instead of trying to confront him about something that may or may not really be a problem, you can talk to about how you need him to meet measurable data points. So your conversation might sound like, "Arjun, I noticed you have a lot of projects left open, I need to you to step it up and get your queue back down to a manageable size." or "I noticed you spent 3 hours yesterday on task that only takes Kabir or Ananya 1 hour. I need you to speed those up, and if you're not familiar with how to do it, I need you to get with one of them to see how you can do it better."
Here you are setting goals instead of fence posts, he will know if he needs to stop spending so much time browsing to reach his goals, then he can find the balance that makes the most sense for him. The important caveat to remember though is that IT is a mental task. It is emotionally and psychologically draining; so, while a CRM is good for tracking your projects, make sure to use it as a means to set goals and stay motivated, and not to let it degrade to the knife you hold above thier heads, because if anything drives an IT guy be less productive, it is feeling like they have goals they can not meet.
As for goal setting: There is a metic often used by sales managers that states that all minimum goals should be meet 80% of the time. What this does is it keeps your minimum goals hard enough to motivate them to do what it right, but easy enough that people don't loose hope or feel like they need to cheat the system to reach them. Goals should also not be a moving target. Once you feel you have a good gauge on what your people can do, set a goal and see how it works for at least 6 months before revisiting it.