This side-mission can be found by entering the Normandy’s galaxy map and having the ship travel to the following location:
Crescent Nebula > Zelene > Helyme.
Scan the planet and locate the anomoly to begin the mission.
After landing, continue away from the landing pad and through the small tunnel here. Investigate the cargo computer terminal. Continue into the doorway on the right and immediately take cover. Defend yourself against a group of Eclipse Vanguards and Troopers. After they are dead, check the passage leading outside to the left for a canister of Refined Palladium . Return inside and bypass the security on the locked door.
Enter the room and take cover. Eliminate the Vanguards and Troopers in the immediate area before following the room to the right, and around to the left across a bridge. Continue to kill anything that gets in your way.
When the room is clear, head to the opposite side of the area from where you entered and activate the bridge control. Use the bridge to access a canister of Refined Palladium .
When you are ready to continue, find the mainframe at the back of the area and bypass the security on it. Once successful, choose the decryption option.
Afterwards, you will now have to defend the mainframe against a few waves of Eclipse attacks; they come in the standard Vanguard and Trooper flavours with a Commander thrown in (shield and armor). Use the cover on the raised platform behind the panel you are decrypting for a decent vantage point over the area. Once you have killed all the baddies, the decryption will magically complete itself.
Use the mainframe again to complete the mission.