Later today a million visitors to PCGamer.com with an eligible Steam account can get a free Steam key. We're giving away five games in the next five weeks, each available for seven days before being replaced, with a million Steam keys up for grabs every time.

Zachtronics Industries' SpaceChem will be our first giveaway. We gave this excellent puzzle game a score of 89 when it was released, and you can grab yourself a copy at 4PM BST today. A different free game from Bundle Stars will follow on each subsequent Wednesday, and you can expect a lot of variety from the lineup.

The redemption method involves giving a single Facebook like/follow to the presented Facebook/Twitter account. Once that's done you can pluck your Steam key from the page and redeem it right away.

We're running the giveaway in association with Bundle Stars , who sell games individually, but specialise in bundling them together to sell them with greater discounts. Over the coming weeks you'll be able to build a free Steam bundle from our super-secret lineup. After SpaceChem, there are four games to go. Come back each week to find out what they are, and be sure to pop by later today to get SpaceChem, which is a very neat game that looks like this: